                 FOR PUBLICATION
 UNITED STATES COURT OF APPEALS
      FOR THE NINTH CIRCUIT

LAURIE TSAO, AKA Laurie Chang,        
               Plaintiff-Appellant,          No. 09-16233
               v.                             D.C. No.
                                          2:08-cv-00713-RCJ-
DESERT PALACE, INC.; T. CRUMRINE,                GWF
            Defendants-Appellees.
                                      

LAURIE TSAO, AKA Laurie Chang,              No. 09-17535
               Plaintiff-Appellant,            D.C. No.
               v.                        2:08-cv-00713-RCJ-
DESERT PALACE, INC.; T. CRUMRINE,                GWF
            Defendants-Appellees.
                                              OPINION

       Appeal from the United States District Court
                for the District of Nevada
       Robert Clive Jones, District Judge, Presiding

          Argued and Submitted October 7, 2010
                San Francisco, California
            Submission Vacated May 24, 2012

                  Argued and Submitted
           June 21, 2012—Pasadena, California

                  Filed October 23, 2012




                           12841
12842               TSAO v. DESERT PALACE, INC.
Before: Alex Kozinski, Chief Judge,* Stephen Reinhardt and
             Marsha S. Berzon, Circuit Judges.

                    Opinion by Judge Berzon




  *Following the death of Judge Louis Pollak of the Eastern District of
Pennsylvania, who was initially a member of the panel, Chief Judge
Kozinski was drawn to replace him and the case was reheard before the
newly constituted panel.
                TSAO v. DESERT PALACE, INC.          12845




                       COUNSEL

Robert A. Nersesian of Nersesian and Sankiewicz, Las Vegas,
Nevada, for plaintiff-appellant Laurie Tsao.

Thomas D. Dillard, Philip S. Gerson, and David M. Jones of
Olson, Cannon, Gormley & Desruisseaux, Las Vegas,
Nevada, for defendant-appellee Desert Palace, Inc.
12846               TSAO v. DESERT PALACE, INC.
Micah S. Echols and Craig R. Anderson of Marquis & Aur-
bach, Las Vegas, Nevada, for defendant-appellee Travis
Crumrine.


                              OPINION

BERZON, Circuit Judge:

   Plaintiff-Appellant Laurie Tsao is a so-called “advantage”
gambler—a professional gambler who uses legal techniques,
such as card counting, to win at casino table games, especially
blackjack.1 She was arrested at Caesars Palace (a casino
owned by the Defendant-Appellee Desert Palace) for trespass-
ing and obstructing the duties of a police officer, and now
challenges that arrest as unconstitutional and as constituting
various common law torts. The District Court held that the
casino’s security guard (non-party Clint Makeley) had proba-
ble cause to make a citizen’s arrest of Tsao for criminal tres-
passing; that Las Vegas Metro Police Officer Travis
Crumrine, a Defendant-Appellee, had probable cause to arrest
Tsao for obstructing the duties of a police officer; and that the
probable cause determinations barred Tsao’s various claims
for relief against Crumrine and Desert Palace. Tsao appeals
those holdings and also the District Court’s grant of attorneys’
fees to Crumrine, as well as the award of certain costs to both
defendants.
  1
   As the District Court noted in its opinion, Tsao and her husband, John
Chang, were members of the so-called MIT Blackjack Team, depicted in
the book “Bringing Down the House” and the movie based on it, “21.” See
also MIT Blackjack Team, Wikipedia, http://en.wikipedia.org/wiki/MIT_
Blackjack_Team (last visited August 2, 2012).
  “Card counting is a mathematical process which enables the player to
achieve better odds when playing blackjack.” Chen v. Nev. State Gaming
Control Bd., 994 P.2d 1151, 1152 n.1 (Nev. 2000) (en banc). “[A]n
‘advantage gambler’ . . . is a regular net winner in Las Vegas casinos.”
Fayer v. Vaughn, 649 F.3d 1061, 1063 (9th Cir. 2011) (per curiam).
                     TSAO v. DESERT PALACE, INC.                    12847
I.       BACKGROUND2

     A.   Casinos & “advantage” players

   This case grows out of the high-stakes cat-and-mouse game
played between advantage gamblers and Desert Palace (some-
times referred to as “the casino”), which operates a number of
gambling venues, including Caesars Palace in Las Vegas.
Desert Palace attempts to identify advantage players and
“trespass” them—that is, tell them to leave and not return—
from the casino’s property. Under Nevada’s trespass statute,
Nevada Revised Statute (“NRS”) § 207.200, returning to a
location from which one has been told not to return by a prop-
erty owner or its agent, or remaining after having been asked
to leave, is a misdemeanor. To avoid being trespassed, or,
once trespassed, to avoid being charged with misdemeanor
trespassing, advantage players apparently take a number of
steps to evade detection, including wearing disguises, obtain-
ing player’s cards in false names, and gambling with the play-
er’s cards of friends and family.3

     B.   Desert Palace Security and the Summons in Lieu of
          Arrest Program

     Once a Desert Palace casino has identified a patron as an
     2
     Because we are reviewing the District Court’s decision to grant the
defendants’ motions for summary judgment, we present the facts here in
the light most favorable to the non-moving party, Tsao. See Luchtel v.
Hagemann, 623 F.3d 975, 978 (9th Cir. 2010).
   3
     We do not address the legality of these actions, as that issue is not
before us. Cf. Chen, 994 P.2d at 1152 (holding that a patron playing under
an alias and with a player’s card obtained with a false passport did not
commit fraud); id. at 1153 (Maupin, J., dissenting) (“[N]either card count-
ing nor the use of a legal subterfuge such as a disguise to gain access to
this table game [blackjack] is illegal under Nevada law.”); see also Fayer,
649 F.3d at 1064 n.3 (discussing Nevada law prohibiting “the possession
of identification documents or information for the purpose of establishing
a false identity” (emphasis and citation omitted)).
12848                 TSAO v. DESERT PALACE, INC.
advantage player, it typically instructs its security guards to
escort that individual from the premises and warn her against
returning. Desert Palace also directs its security to identify
individuals who have returned despite having received a tres-
pass warning. Pursuant to the policies in effect at Caesars Pal-
ace at all times relevant to this suit, if a previously trespassed
individual returned to the casino, the security supervisor had
the discretion to escort the individual from the casino with a
second warning; to effect a citizen’s arrest for trespassing;4 or
to issue a citation to appear in court to answer for the crime
of misdemeanor trespassing.

   Private security guards, of course, typically do not have the
ability to issue citations for criminal offenses. Some of the
security guards at Caesars Palace, however, have the authority
to issue a summons5 in lieu of arrest (“SILA”). To obtain this
authority, private casino security guards must take a training
course given by the Las Vegas Metro Police Department
(“LVMPD”). During his deposition, Officer Crumrine
explained that the LVMPD invites the security personnel of
the city’s casinos and department stores to take part in the
SILA program “[t]o alleviate some of the manpower concerns
  4
     Section 171.126(1) of Nevada’s Revised Statutes authorizes a citizen’s
arrest “[f]or a public offense committed or attempted in the person’s pres-
ence.” Misdemeanor trespassing, as defined in NRS § 207.200, is consid-
ered a public offense. See NRS § 206.140(2).
   5
     Technically, the guards are authorized to issue a “citation,” rather than
a “summons.” Compare Black’s Law Dictionary (9th ed. 2009) (defining
a “citation” as “1. A court-issued writ that commands a person to appear
at a certain time and place to do something demanded in the writ, or to
show cause for not doing so. 2. A police-issued order to appear before a
judge on a given date to defend against a stated charge, such as a traffic
violation.”) with id. (defining “summons” as, inter alia, “1. A writ or pro-
cess commencing the plaintiff’s action and requiring the defendant to
appear and answer. 2. A notice requiring a person to appear in court as a
juror or witness.”); see also NRS § 171.1773 (specifying the form and
contents of a citation). The parties, however, refer to it as a “summons.”
We use the two terms interchangeably.
                    TSAO v. DESERT PALACE, INC.                    12849
of the police” by relieving local law enforcement of the obli-
gation to respond to calls regarding relatively minor crimes.

   After being trained, the security guards can issue summon-
ses for criminal trespassing,6 so long as the suspect is posi-
tively identified; not under the influence of intoxicating
substances; cooperative; and free of outstanding arrest war-
rants. The guards verify that a particular individual does not
have outstanding warrants by calling the records department
of the LVMPD. A citation issued by a Caesars Palace security
guard looks no different from one given by an LVMPD offi-
cer: it commands the suspect’s appearance in court on a speci-
fied date and time, and states, accurately, that the failure to
appear constitutes a separate offense. See NRS
§ 171.17785(1) (“It is unlawful for a person to violate a writ-
ten promise to appear given to a peace officer upon the issu-
ance of a misdemeanor citation . . . .”); Las Vegas Municipal
Code (“LVMC”) § 1.20.060 (2009) (“When an accused signs
a citation promising to appear at the time and place specified
in the citation and fails to appear as promised, the Court shall
issue and have delivered for execution a warrant for his
arrest.”).

   After the SILA officer has issued the citation, Nevada law
requires that it be filed “with a court having jurisdiction over
the alleged offense.” NRS § 171.1776(1). The Justice Courts
have jurisdiction over all misdemeanors, including the
offenses for which the SILA officers may issue citations. See
NRS § 4.370(3); Parsons v. Fifth Jud. Dist. Ct. of Nev., In &
For Cnty. of Nye [“Parsons I”], 885 P.2d 1316, 1319 (Nev.
1994), overruled on other grounds by Parsons v. State
[“Parsons II”], 10 P.3d 836 (Nev. 2000) (en banc). Once
properly filed, the citation is “deemed to be a lawful com-
plaint for the purpose of prosecution.” NRS § 171.1778.
  6
   According to Officer Crumrine, SILA officers can also issue summon-
ses for petty larceny and defrauding an innkeeper. The record is silent as
to whether they can issue a summons for other crimes.
12850             TSAO v. DESERT PALACE, INC.
While Nevada law requires many public offenses to be prose-
cuted by indictment or information, there is an exception for
offenses tried in Justice Courts, which are prosecuted by com-
plaint. NRS § 172.015. Taken together, these features of
Nevada law mean that a misdemeanor citation issued by a
SILA officer not only initiates the formal criminal justice pro-
cess by informing the court of the alleged criminal violation
and commanding the defendant’s presence, but also serves as
the state’s own charging document. See NRS §§ 4.370(3),
171.1776(1), 171.1778, 172.015; Parsons I, 885 P.2d at
1319-20.

   In sum, SILA officers have the authority to issue citations
that compel individuals to appear in a particular Nevada Jus-
tice Court at a specified date and time, thereby performing a
law enforcement function. See Flagg Bros., Inc. v. Brooks,
436 U.S. 149, 163-64, 163 n.14 (1978). When they do appear
in the Justice Courts, the accused must defend against the
criminal charges levied by the officer who issued the citation;
in this respect, the SILA officers also perform a prosecutorial
or quasi-prosecutorial function. See Robertson v. United
States ex rel. Watson, 130 S. Ct. 2184, 2185-87 (2010) (per
curiam) (Roberts, C.J., dissenting from the dismissal of the
writ of certiorari as improvidently granted) (suggesting that
criminal prosecutions may only be brought “in the name and
pursuant to the power of the [state]”).

  C.    Tsao’s arrest by Desert Palace

   Laurie Tsao is a professional gambler, apparently quite a
good one. Tsao has received several trespass warnings. Prior
to her arrest at Caesars Palace, she had been “trespassed”
from Desert Palace properties on at least five occasions under
four different names: Cao Hong, Laurie Cao, Laurie Tsao, and
Shuyu Deng. On each occasion, she was told that she was not
welcome on any of the casino’s properties, including Caesars
Palace, and was warned that she could be arrested for tres-
passing if she returned. The last of these warnings was given
                     TSAO v. DESERT PALACE, INC.                    12851
by Clint Makeley, the night shift supervisor of Caesars Palace
security, on September 23, 2007.

   Following that warning, but before Tsao was arrested on
March 19, 2008, Desert Palace mailed her at least three pro-
motional offers. The offers were sent to Tsao’s home address
and were directed to “Laurie Tsao.” The first offer, valid from
December 1, 2007 through February 29, 2008, offered a free
four-night stay at one of seven Las Vegas casino hotels
(including Caesars Palace) owned by Desert Palace. The sec-
ond (labeled an “invitation”) was valid from March 19
through March 24, 2008, and offered a three-night stay at one
of the same seven hotels, as well as entry to a “VIP Viewing
Area” to watch college basketball and “VIP access to Race
and Sports Book wagering area.” The third, valid from March
1 through May 31, 2008, included six different offers, includ-
ing one for a free four-night stay at one of Desert Palace’s
casino hotels. Tsao’s claims against Desert Palace turn in
large part on whether these offers can reasonably be viewed
as “invitations” for Tsao to play blackjack at Caesars Palace.

   Tsao returned to Caesars Palace around 2:00 a.m. on March
19, 2008, along with her friend and fellow advantage player
Nelson Fu. Tsao was using a player’s card for someone
named “Monica Lieu,” which she had found abandoned dur-
ing a prior visit. Around 5:00 a.m., someone from the Caesars
Palace surveillance team advised Makeley that a patron on the
property had been trespassed on September 23, 2007, under
the name of “Shuyu Deng.” After reviewing casino records,
Makeley told John Banner, the casino manager, that the
casino could (a) re-trespass and escort Tsao out of the casino;
(b) issue her a SILA if she had identification; or (c) make a
citizen’s arrest for trespassing. Banner and/or Makeley appar-
ently decided to do (b) or (c), depending on whether Tsao had
identification.7
  7
    The record is unclear as to whether Makeley made this decision alone
or if he made it together with Banner. Although Makeley testified at his
deposition that it was his “call,” he also said that he checked with Banner
to see “if he agreed with me or how he wished to pursue with this matter
we have in hand.”
12852             TSAO v. DESERT PALACE, INC.
   As depicted by the casino’s surveillance video (which is
part of the record), Makeley and two other security guards
approached Tsao on the casino floor at approximately 5:18
a.m. Makeley asked her for identification; when Tsao stated
that she had none, Makeley allegedly replied that she would
“rot in jail.” Tsao then asked repeatedly to be permitted to
leave, a request Makeley refused. After arguing with Tsao on
the casino floor, Makeley and the two other security guards
grabbed Tsao by the arm, handcuffed her (even though she
was not behaving aggressively), and led her off the floor,
through the casino, and into an interview room.

   After arresting Tsao, Makeley approached Fu and asked
him for identification. Fu, who apparently had not been previ-
ously trespassed from Caesars Palace, was allowed to leave
with a trespass warning. After leaving the casino, Fu immedi-
ately called Tsao’s husband, John Chang, to inform him of
Tsao’s arrest. Chang then called Robert Nersesian, the cou-
ple’s long-time attorney. Chang advised Nersesian of Tsao’s
arrest and of the previous trespass warning, and said that he
(Chang) had the promotional offers that Caesars Palace had
sent to Tsao. Nersesian immediately met with Chang,
obtained the mailed offers, and proceeded to Caesars Palace.

   Meanwhile, Makeley had called LVMPD to ask for an offi-
cer’s assistance. As he waited for the officer to arrive, Make-
ley began questioning Tsao, who was still in handcuffs. When
Tsao stated that she did not have identification with her,
Makeley asked rhetorically, “Wouldn’t you rather get a ticket
from me and be on your way, rather than go to jail? That’s
your choices. [sic] Carry ID and get the ticket.” When Tsao
asked which ticket Makeley was referencing, Makeley told
her, “I go to all the classes just like the police department. I
get to write you a ticket and get you on your way in no time.”
Tsao stated that she had identification in her car that she could
retrieve, to which Makeley responded, “[i]t doesn’t work that
way.” In response to Tsao’s question, “How am I supposed to
                    TSAO v. DESERT PALACE, INC.                  12853
know that?”, Makeley responded that she should “ask the
judge.”

   Makeley then began questioning Tsao about her identity,
apparently the first time that Tsao was asked for her name.
While that question is a simple one, the answer is complicated
in Tsao’s case. In addition to playing (and having been tres-
passed) under various aliases, Tsao has other reasons for
using different names. Like many other Chinese immigrants,
Tsao took an English first name (Laurie) when she immi-
grated, though she sometimes appends her Chinese first name,
Hong, as either a middle or a second last name. With regard
to her last name, it is translated from a Chinese character; in
her case, the closest English spelling approximation is “Cao,”
which Tsao sometimes uses. However, upon discovering that
many native English speakers pronounce “Cao” as “cow,”
Tsao began also using “Tsao,” which is closer to how her Chi-
nese name ought to be pronounced. Tsao also went for a time
by the last name of “Chen,” the surname of her first husband,
whom she divorced in 1997. After her divorce, she reverted
to using her birth name, Tsao.

  In 2001, Tsao married her current husband, John Chang.
She now sometimes goes by Laurie Chang. Her U.S. passport
was issued to “Laurie Chang.” But she also still uses “Tsao”
as her surname, and her Nevada driver’s license and credit
cards are issued in that name. When questioned by Makeley,
Tsao told him that her name was “Laurie Chang,” although
Makeley seems to have heard the last name as “Chen.”8
  8
   There is evidence in the record suggesting that Laurie gave her sur-
name as “Chang” because she was concerned that the name “Tsao” would
cause her more problems than “Chang.” Tsao also maintains that because
“Chang” is the name on her U.S. passport, she considered it her “highest
and best name.”
12854                TSAO v. DESERT PALACE, INC.
  D.    Officer Crumrine’s arrival

   LVMPD officer (and defendant) Travis Crumrine arrived at
Caesars Palace at approximately 5:45 a.m. As soon as Crum-
rine entered the interview room, Makeley—who knew Crum-
rine from previous calls to which Crumrine had responded—
informed Crumrine that Tsao had given the name “Laurie
Chen,” had been trespassed on September 28, 2007, and had
been playing on that night under an alias. Tsao was, at this
point, still in handcuffs, and remained in handcuffs through-
out the remainder of her time at the casino.

   Crumrine, without ever identifying himself by name or
position or giving any Miranda warnings, began questioning
Tsao while simultaneously rummaging through her purse.
Over the next several minutes, Crumrine questioned Tsao
about how much money she had with her; her occupation;
whether she had been arrested before; her age; why she did
not have identification with her; and how she had arrived at
the casino that night. When Tsao stated that she had driven,
Crumrine asked where her car was parked. Tsao answered
that her car was being driven by a friend. Crumrine then asked
whether Tsao was lying; she answered “maybe.”9 Understand-
ably annoyed, Crumrine told Tsao that “the next question I
ask you is very serious for you not to lie to me, because if you
lie to me, I have to take you to jail. Do you understand?”
After Tsao indicated that she understood, Crumrine asked,
“What’s your last name?” Tsao said that her last name was
“Chang.” After asking Tsao a few more questions about her
identity, including her date of birth, Social Security number,
and the state in which she is licensed to drive—to all of which
Tsao answered truthfully—Crumrine left the room. After
Crumrine left the interview room, he attempted to search for
  9
   Tsao said later that she said “maybe” because she thought it likely that,
by that time, Fu or her husband had moved the vehicle from the Caesars
Palace parking lot, in which case her answer would have been true.
                     TSAO v. DESERT PALACE, INC.                    12855
“Laurie Chang” in the Nevada databases to which he had
access, but the search yielded no results.

   The remainder of Tsao’s time in the interview room, as
portrayed by the video recording, is mostly unremarkable,
except in a few respects. Approximately ten minutes after
Crumrine left the interview room, Tsao asked a casino secur-
ity guard whether Crumrine was a police officer; the guard
said he was. About twelve minutes later, Crumrine returned
to the interview room and began going through Tsao’s purse
once more, at which point he found her car keys. Crumrine
gave the keys to Caesars Palace security guards, instructing
them to try to identify Tsao’s vehicle in the Caesars Palace
parking lot by pushing the “panic” button on the key fob.
According to Crumrine, the ploy worked, and he was ulti-
mately able positively to identify Tsao from the DMV records
associated with her Social Security and license plate numbers.

   At approximately 6:45 a.m., Nersesian arrived at the casino
and spoke to Crumrine. Nersesian first identified himself as
the attorney for “Laurie Tsao,” to which Crumrine responded
that the only person he had in custody was “Laurie Chang.”10
Nersesian explained that Laurie was “transitioning between”
her birth and married names; that she uses both Chang and
Tsao; and that Nersesian could have Mr. Chang on the prem-
ises within five minutes to confirm that Tsao uses both names.
Nersesian showed Crumrine the promotional offers that
Desert Palace had sent Tsao since she was last trespassed,
explaining that the offers rescinded any prior trespass warn-
ing. Crumrine responded only that Nersesian’s argument was
“pretty weak.” Before the conversation ended, Nersesian
asked if Tsao could simply be given a summons, rather than
be arrested, an option Crumrine refused.11 Immediately after
  10
      The record indicates that by the time he spoke to Nersesian, Crumrine
likely knew that the woman being held in the interview room was, in fact,
Laurie Tsao.
   11
      At oral argument on appeal, Crumrine’s attorney suggested that Crum-
rine could not simply release Tsao with a citation after detaining her for
12856                TSAO v. DESERT PALACE, INC.
his encounter with Nersesian, Crumrine told Makeley, who
had not been privy to the conversation, that it “might have
been a mistake” to talk to Nersesian at all.

   Tsao was finally escorted out of the interview room around
7:30 a.m., about an hour and forty minutes after Crumrine
arrived. At some point, she was given a summons for misde-
meanor trespassing. Although the record is unclear as to when
the summons was written or when she received it, both Make-
ley and Crumrine signed their names in the box marked “Offi-
cer/Complainant’s Signature.”12

   Crumrine took Tsao to the Clark County Detention Center.
While booking her, he explained that she was under arrest for
providing false information to a police officer, NRS
§ 197.190. Tsao spent approximately ten hours in the Clark
County Detention Center. The prosecutor later dismissed both
the trespassing charge and the charge for providing false
information to a police officer.

  E.    The litigation

  Tsao filed suit on May 9, 2008 in Nevada state court
against Desert Palace and Crumrine, requesting compensatory

as long as he had because, under Nevada law, temporary detentions of
more than sixty minutes are per se unreasonable. See NRS § 171.123(4);
State v. McKellips, 49 P.3d 655, 660 (Nev. 2002) (“[U]nder NRS 171.123,
once an individual has been detained, the officer has sixty minutes to
either release or arrest the individual.”); Barrios-Lomeli v. State, 961 P.2d
750, 750 (Nev. 1998) (“According to NRS 171.123(4), a detention longer
than sixty minutes is unreasonable per se.”).
   12
      Desert Palace argues that Crumrine signed the summons as a witness
only. Because both names appear in the same box, with no designation of
one or the other as the complainant and the other as witness, a jury would
certainly be entitled to conclude that both signed in the same capacity. On
summary judgment, we must take the facts in the light most favorable to
Tsao.
                     TSAO v. DESERT PALACE, INC.                     12857
and punitive damages. She alleged several claims for relief
applicable to both defendants, including a constitutional claim
under 42 U.S.C. § 1983 for unreasonable search and seizure
and claims for the common-law torts of battery, false impris-
onment, and defamation. Three other claims—for common-
law assault, premises liability, and abuse of process—were
directed solely at Desert Palace.13

   The case was timely removed to the District Court for the
District of Nevada. The District Court denied Tsao’s motion
for partial summary judgment as to Desert Palace’s liability
for false imprisonment, which was premised on the argument
that the casino could not lawfully give Tsao a trespass warn-
ing. Later, the District Court entered an order denying Tsao’s
second motion for partial summary judgment (directed at both
defendants) and granting summary judgment to the defen-
dants on all counts. Finally, in a third order, the District Court
granted Crumrine’s motion for $1,474.80 in costs and
$15,000 in attorneys’ fees, finding that Tsao’s claims were
“frivolous, unreasonable, and without foundation.” On the
same day, the District Court granted Desert Palace $4,049.48
in costs.

   Tsao timely appealed all three orders.

                            DISCUSSION

   Tsao’s claims arise from two discrete arrests, although their
timing and the events leading up to them were closely related.
The claims against Desert Palace concern the arrest effected
  13
     Tsao also alleged a claim against both defendants for the intentional
infliction of emotional distress, but she abandoned it on appeal. Addition-
ally, while the District Court construed Tsao’s complaint as stating a Fifth
Amendment claim against Crumrine for the alleged violation of Tsao’s
Miranda rights, Tsao did not argue in her opening brief that the District
Court’s dismissal of that claim was erroneous, thereby waiving appeal of
that issue. See Blanford v. Sacramento County, 406 F.3d 1110, 1114 n.8
(9th Cir. 2005); Smith v. Marsh, 194 F.3d 1045, 1052 (9th Cir. 1999).
12858               TSAO v. DESERT PALACE, INC.
by its security supervisor, Clint Makeley, for trespassing
under NRS § 207.200; those against Crumrine are premised
on his arrest of Tsao for obstructing his investigation by pro-
viding false information, in violation of NRS § 197.90.

   The District Court held that the undisputed facts established
that probable cause supported each of the arrests, thereby enti-
tling the defendants to summary judgment on all claims as a
matter of law. See Atwater v. City of Lago Vista, 532 U.S.
318, 354 (2001). We affirm the District Court’s grant of sum-
mary judgment to Crumrine on Tsao’s § 1983 claim. We also
conclude, albeit on somewhat different grounds than those
relied upon by the District Court, that Desert Palace is entitled
to summary judgment on Tsao’s § 1983 claims. Because our
holding on the § 1983 claims resolves all the federal claims
but alters the circumstances in which the District Court
decided to exercise supplemental jurisdiction over the state
law claims, see 28 U.S.C. § 1367, we remand the state law
claims to the District Court to consider whether it wishes to
continue exercising jurisdiction over them, in which case it
would have to reconsider its conclusions regarding the viabil-
ity of the state law causes of action in light of legal principles
it did not take into account.

     We consider the federal claims first.

I.    Claims under 42 U.S.C. § 1983

   “To establish § 1983 liability, a plaintiff must show both
(1) deprivation of a right secured by the Constitution and laws
of the United States, and (2) that the deprivation was commit-
ted by a person acting under color of state law.” Chudacoff v.
Univ. Med. Ctr. of S. Nev., 649 F.3d 1143, 1149 (9th Cir.
2011). The crux of Tsao’s § 1983 claims against both Desert
Palace and Crumrine is that each violated her Fourth Amend-
ment right to be free of unreasonable searches and seizures
while acting under color of state law.
                  TSAO v. DESERT PALACE, INC.              12859
  A.   Desert Palace

   Tsao alleges that her arrest and detention for trespassing by
Desert Palace, acting through Makeley, were without proba-
ble cause because the casino had invited her to return to the
premises through the promotional offers. Because Tsao has
sued Desert Palace and not Makeley, we must initially address
whether the suit against Desert Palace could be proper.

   [1] To decide that question, we begin by considering, for
the first time in this circuit, whether Monell v. Dep’t of Soc.
Servs., 436 U.S. 658, 691 (1978), applies to suits against pri-
vate entities under § 1983. In Monell, the Supreme Court held
that municipalities and other local government units could be
sued for constitutional violations under § 1983. Id. at 690.
The court also held, however, that “a municipality cannot be
held liable solely because it employs a tortfeasor—or, in other
words . . . on a respondeat superior theory.” Id. at 691
(emphasis in original). To create liability under § 1983, the
constitutional violation must be caused by “a policy, practice,
or custom of the entity,” Dougherty v. City of Covina, 654
F.3d 892, 900 (9th Cir. 2011), or be the result of an order by
a policy-making officer, see Gibson v. County of Washoe, 290
F.3d 1175, 1186 (9th Cir. 2002). Whether Monell applies to
suits against private entities under § 1983 is a threshold ques-
tion with regard to Desert Palace’s liability because, if it does,
Monell establishes the parameters of such liability.

   [2] Every one of our sister circuits to have considered the
issue has concluded that the requirements of Monell do apply
to suits against private entities under § 1983. See Buckner v.
Toro, 116 F.3d 450, 453 (11th Cir. 1997); Street v. Corr.
Corp. of Am., 102 F.3d 810, 818 (6th Cir. 1996); Rojas v.
Alexander’s Dep’t Store, Inc., 924 F.2d 406, 408-09 (2d Cir.
1990); Lux v. Hansen, 886 F.2d 1064, 1067 (8th Cir. 1989);
Iskander v. Vill. of Forest Park, 690 F.2d 126, 128-29 (7th
Cir. 1982); Lusby v. T.G. & Y. Stores, Inc., 749 F.2d 1423,
1433 (10th Cir. 1984), vacated on other grounds sub nom.
12860             TSAO v. DESERT PALACE, INC.
City of Lawton v. Lusby, 474 U.S. 805 (1985); Powell v.
Shopco Laurel Co., 678 F.2d 504, 506 (4th Cir. 1982); see
also Benn v. Universal Health Sys., Inc., 371 F.3d 165, 174
(3d Cir. 2004); Lyons v. Nat’l Car Rental Sys., Inc., 30 F.3d
240, 246 (1st Cir. 1994). Like those circuits, we see no basis
in the reasoning underlying Monell to distinguish between
municipalities and private entities acting under color of state
law.

   As Monell observed, the text of § 1983 “cannot be easily
read to impose liability vicariously on governing bodies solely
on the basis of the existence of an employer-employee rela-
tionship with a tortfeasor.” 436 U.S. at 692. On the contrary,
the Court observed, Congress explicitly provided “that A’s
tort became B’s liability if B ‘caused’ A to subject another to
a tort.” Id. Thus, the Court held, “constitutional deprivations”
could subject a municipality to liability under § 1983 if they
were the result of a “governmental ‘custom’ ” sufficient to
establish causation. Id. at 690-91. It would be odd indeed to
suggest that this interpretation has less force in the context of
a suit against a private entity. See Powell, 678 F.2d at 506
(“No element of the Court’s ratio decidendi lends support for
distinguishing the case of a private corporation.”).

  [3] To make out a claim against Desert Palace under
Monell, Tsao must show that (1) Desert Palace acted under
color of state law, and (2) if a constitutional violation
occurred, the violation was caused by an official policy or
custom of Desert Palace. See Harper v. City of Los Angeles,
533 F.3d 1010, 1024 (9th Cir. 2008). We address each
requirement in turn.

    i.   Color of state law

   Desert Palace is a private corporation. Although § 1983
makes liable only those who act “under color of” state law,
“even a private entity can, in certain circumstances, be subject
to liability under section 1983.” Villegas v. Gilroy Garlic Fes-
                      TSAO v. DESERT PALACE, INC.                     12861
tival Ass’n, 541 F.3d 950, 954 (9th Cir. 2008) (en banc). Spe-
cifically, a plaintiff must show that “the conduct allegedly
causing the deprivation of a federal right [was] fairly attribut-
able to the State.” Lugar v. Edmondson Oil Co., 457 U.S. 922,
937 (1982). “The Supreme Court has articulated four tests for
determining whether a private [party’s] actions amount to
state action: (1) the public function test; (2) the joint action
test; (3) the state compulsion test; and (4) the governmental
nexus test.” Franklin v. Fox, 312 F.3d 423, 444-45 (9th Cir.
2002). We hold that Desert Palace’s actions are “fairly attrib-
utable to the state” under the joint action test.14

   [4] The joint action test asks “ ‘whether state officials and
private parties have acted in concert in effecting a particular
deprivation of constitutional rights.’ ” Id. at 445 (quoting Gal-
lagher v. Neil Young Freedom Concert, 49 F.3d 1442, 1453
(10th Cir. 1995)). This requirement can be satisfied either “by
proving the existence of a conspiracy or by showing that the
private party was ‘a willful participant in joint action with the
State or its agents.’ ” Id. (quoting Collins v. Womancare, 878
F.2d 1145, 1154 (9th Cir. 1989)). Ultimately, joint action
exists when the state has “ ‘so far insinuated itself into a posi-
tion of interdependence with [the private entity] that it must
be recognized as a joint participant in the challenged activi-
ty.’ ” Gorenc v. Salt River Project Agric. Improvement &
Power Dist., 869 F.2d 503, 507 (9th Cir. 1989) (alteration in
original) (quoting Burton v. Wilmington Parking Auth., 365
U.S. 715, 725 (1961)). Particularly relevant here is the maxim
that “if the state ‘knowingly accepts the benefits derived from
unconstitutional behavior,’ . . . then the conduct can be treated
as state action.” Id. (quoting Nat’l Collegiate Athletic Ass’n v.
Tarkanian, 488 U.S. 179, 192 (1988)).

   [5] Desert Palace’s behavior qualifies as state action under
  14
    In view of our conclusion, we need not consider whether Tsao’s alle-
gations are sufficient to meet the public function test or either of the other
two tests for state action.
12862             TSAO v. DESERT PALACE, INC.
the joint action test thanks to its system of cooperation and
interdependence with the LVMPD. First, under the SILA pro-
gram, some Desert Palace security personnel have the author-
ity, normally reserved to the state, to issue a citation to appear
in court for the crime of misdemeanor trespassing. To gain
this authority, security guards must take a training course
given by the LVMPD. This delegation of authority by the
police department, Crumrine explained, helps “alleviate some
of the manpower concerns of the police” by relieving them
from responding to every claim of trespassing that arises at a
casino. Security guards with SILA authority may not arrest a
suspect who has an outstanding arrest warrant, so they rou-
tinely call the LVMPD’s records department to get informa-
tion concerning warrants. The citations that security guards
issue are no different from those issued by police officers, and
failure to respond to them by appearing in court constitutes a
separate offense. See NRS § 171.17785(1).

   [6] Desert Palace and the state are therefore joint partici-
pants in the SILA program, which produces benefits that
accrue to both Desert Palace and the LVMPD. See Tarkanian,
488 U.S. at 192. By training Desert Palace security guards,
providing information from the records department, and dele-
gating the authority to issue citations, the State has “so far
insinuated itself into a position of interdependence with
[Desert Palace] that it must be recognized as a joint partici-
pant in the challenged activity.” Gorenc, 869 F.2d at 507.

   The existence of SILA authority pervasively affected
Makeley’s interactions with Tsao. When Makeley dealt with
Tsao, he was in a position to invoke his SILA authority to jus-
tify his actions, giving Tsao the (accurate) impression that he
was “clothed with the authority of state law,” Williams v.
United States, 341 U.S. 97, 99 (1951). For example, when
Tsao told Makeley on the casino floor that she did not have
identification, he told her that she would “rot in jail.” Back in
the interview room, Makeley informed Tsao that because he
“go[es] to all the classes just like the police department,” he
                  TSAO v. DESERT PALACE, INC.              12863
“get[s] to write . . . tickets” just like they do, and that her
options were to “carry ID and get the ticket” or “go to jail.”
When Tsao complained that she did not know that she had to
carry identification, Makeley told her that she would have to
tell it to “the judge.”

   [7] Furthermore, as the facts of this case illustrate, Make-
ley’s ultimate decision to make what was in form a citizens’
arrest is part and parcel of the overall trespass enforcement
program established by Desert Palace and LVMPD jointly.
Under that program, Desert Palace security guards may not
issue a citation unless they are able to identify their suspect.
Makeley testified that he decided before he approached Tsao
that he would either issue her a SILA or make a citizen’s
arrest for trespassing, depending on whether he could identify
her. Desert Palace’s trespass enforcement program therefore
depended in its basic format on the cloak of state authority
under which it operated.

   Lusby v. T.G. & Y. Stores, Inc., 749 F.2d 1423 (10th Cir.
1984), is instructive in this regard. In that case, the Tenth Cir-
cuit held that an off-duty police officer employed as a security
guard was a state actor when he made a citizen’s arrest for
shoplifting. Id. at 1429. Notably, the security guard told the
plaintiff that “he was going to jail,” and the police department
provided the store that employed him “with special forms pre-
pared for merchants who detained suspected shoplifters which
apparently allowed officers the discretion to issue a summons
to a suspect . . . without taking the person to jail.” Id. at
1429-30. Thus, “the local police followed a policy that
allowed [the security guard] to substitute his judgment for that
of the police.” Id. at 1430. “Such cooperative activity between
the police department and a private party,” the court con-
cluded, “is sufficient to make [the guard] a party acting under
color of state law.” Id.

  Just as in Lusby, Makeley did more than effectuate a citi-
zen’s arrest—he purported to act on behalf of the state from
12864             TSAO v. DESERT PALACE, INC.
the outset of the encounter. That pretense, although not con-
clusive, supports Tsao’s contention that Makeley was a state
actor for purposes of § 1983. See Griffin v. Maryland, 378
U.S. 130, 135 (1964) (“If an individual is possessed of state
authority and purports to act under that authority, his action
is state action. It is irrelevant that he might have taken the
same action had he acted in a purely private capacity . . . .”);
see also Flagg Bros., 436 U.S. at 163 n.14; Traver v. Meshriy,
627 F.2d 934, 938 (9th Cir. 1980) (holding that an off-duty
police officer employed as a bank security guard acted under
color of law when he identified himself as a police officer to
a bank robbery suspect); United States v. Temple, 447 F.3d
130, 139 (2d Cir. 2006).

   Given the particular characteristics of Desert Palace’s pro-
gram for ousting unwanted gamblers, the District Court’s reli-
ance on Collins v. Womancare, 878 F.2d at 1154, to reject the
existence of state action was misplaced. In Collins, an abor-
tion provider obtained an injunction prohibiting certain indi-
viduals from protesting immediately in front of its offices.
878 F.2d at 1146. When protestors not subject to the injunc-
tion demonstrated in front of the abortion provider, two of its
employees effected a citizen’s arrest and turned the protestors
over to a waiting policeman. Id. We held that the employees
who made the arrest were not state actors, as the police played
no role in initiating the arrests, conducted independent inves-
tigations, and maintained a policy of neutrality throughout.
Consequently, the state had not “so far insinuated itself into
a position of interdependence with [the defendant’s employ-
ees] that it must be recognized as a joint participant in the
challenged activity.” Id. at 1155 (internal quotation marks
omitted).

   [8] Unlike in Collins, Makeley invoked the authority of the
state throughout the encounter with Tsao, stressing his author-
ity under the SILA program. Then, Makeley and Crumrine
acted in concert from the time Crumrine arrived at the casino.
Crumrine did not simply effectuate a citizen’s arrest that had
                  TSAO v. DESERT PALACE, INC.            12865
already been made, maintaining his neutrality throughout, nor
did he “refuse[ ] . . . to arrest [Tsao] on his own authority.”
878 F.2d at 1155. Rather, he entered the room where Makeley
was questioning Tsao and took over the investigation into
Tsao’s identity. Crumrine asked numerous questions,
searched Tsao’s purse and pockets, and talked to her lawyer
when he arrived. Crumrine also directed Desert Palace secur-
ity guards to locate Tsao’s car, which helped him determine
her identity. Eventually, Crumrine and Makeley both signed
the summons Tsao received for misdemeanor trespassing.
Makeley, and therefore Desert Palace (if it was otherwise lia-
ble), was without a doubt engaged in joint action with the
LVMPD when Makeley detained, investigated, arrested, and
cited Tsao.

  Because we conclude that Desert Palace was a state actor,
we must next consider whether the casino violated Tsao’s
constitutional rights.

     ii.   Constitutional deprivation

  Desert Palace arrested Tsao for trespassing in violation of
NRS § 207.200. Tsao argues that this arrest violated her
Fourth Amendment rights because it was not supported by
probable cause. See United States v. Thornton, 710 F.2d 513,
515 (9th Cir. 1983).

   Tsao had been ejected from Caesars Palace at least five
times, most recently on September 23, 2007. If that were the
end of the matter, it would be clear that she trespassed when
she returned on March 19, 2008. See NRS § 207.200(1)(b);
see also Jordan v. State ex rel. DMV & Pub. Safety, 110 P.3d
30, 47 (Nev. 2005), overruled on other grounds by Buzz Stew,
LLC v. City of N. Las Vegas, 181 P.3d 670 (Nev. 2008). Tsao
argues, however, that the promotional offers from Desert Pal-
ace effectively rescinded the earlier trespass warnings and
invited her back onto the property, and that she therefore was
not trespassing when she returned. The District Court rejected
12866             TSAO v. DESERT PALACE, INC.
this argument, holding that (1) the promotional offers were
not sufficient to rescind the earlier trespass warning as a mat-
ter of law; and (2) even if the promotional offers did represent
consent to Tsao’s visit, Makeley still had probable cause to
believe Tsao was trespassing because he was not aware of
them.

   As an initial matter, Makeley’s ignorance of the invitations
was not sufficient to defeat Tsao’s constitutional claim. Her
suit is against Desert Palace, not Makeley. We have repeat-
edly held that “[i]f a plaintiff establishes he suffered a consti-
tutional injury by the City, the fact that individual officers are
exonerated is immaterial to liability under § 1983.” Fairley,
281 F.3d at 917. Fairley applied this rule to Fourth Amend-
ment claims for arrest without probable cause, also at issue
here, and made clear that the rule applies “whether the offi-
cers are exonerated on the basis of qualified immunity,
because they were merely negligent, or for other failure of
proof.” Id. at 916-17, 917 n.4 (citing Chew v. Gates, 27 F.3d
1432, 1438 (9th Cir. 1994)).

   Simply put, the fact that Makeley himself may have had
probable cause to arrest Tsao is irrelevant in a suit against
Desert Palace. See Restatement (Third) of Agency § 7.04 cmt.
b (“If the agent’s conduct is not tortious, the principal is sub-
ject to liability if the same conduct on the part of the principal
would have subjected the principal to tort liability. For exam-
ple, an agent’s action may not be tortious because the agent
lacks information known to the principal.”). Assuming the
promotional offers were legally sufficient to constitute an
invitation, Makeley’s ignorance of them has no bearing on
whether Desert Palace, if otherwise liable, violated Tsao’s
Fourth Amendment rights.

   Whether the invitations Tsao received from Desert Palace
were sufficient to consent to her presence at the blackjack
table is, as we explain later, a much more complicated issue,
one that involves novel questions of state law. See pg. 12878
                  TSAO v. DESERT PALACE, INC.              12867
infra. Because we conclude that Tsao has not sufficiently
alleged an “official policy, custom, or pattern” on the part of
Desert Palace involving such invitations, we need not reach
that state law issue, and do not do so.

    iii.   Official policy, custom, or pattern

   [9] Tsao must demonstrate that an “official policy, custom,
or pattern” on the part of Desert Palace was “the actionable
cause of the claimed injury.” Harper, 533 F.3d at 1022, 1026.
A “policy” is “ ‘a deliberate choice to follow a course of
action . . . made from among various alternatives by the offi-
cial or officials responsible for establishing final policy with
respect to the subject matter in question.’ ” Long v. Cnty. of
Los Angeles, 442 F.3d 1178, 1185 (9th Cir. 2006) (alteration
in original) (quoting Fairley, 281 F.2d at 918). Gibson v.
County of Washoe discussed two types of policies: those that
result in the municipality itself violating someone’s constitu-
tional rights or instructing its employees to do so, and those
that result, through omission, in municipal responsibility “for
a constitutional violation committed by one of its employees,
even though the municipality’s policies were facially constitu-
tional, the municipality did not direct the employee to take the
unconstitutional action, and the municipality did not have the
state of mind required to prove the underlying violation.” 290
F.3d at 1185-86 (citing City of Canton v. Harris, 489 U.S.
378, 387-89 (1989)). We have referred to these two types of
policies as policies of action and inaction. Long, 442 F.3d at
1185.

   [10] A policy of inaction or omission may be based on fail-
ure to implement procedural safeguards to prevent constitu-
tional violations. Oviatt v. Pearce, 954 F.2d 1470, 1477 (9th
Cir. 1992). To establish that there is a policy based on a fail-
ure to preserve constitutional rights, a plaintiff must show, in
addition to a constitutional violation, “that this policy
‘amounts to deliberate indifference’ to the plaintiff’s constitu-
tional right[,]” Id. at 1474 (quoting Canton, 489 U.S. at 389),
12868             TSAO v. DESERT PALACE, INC.
and that the policy caused the violation, “in the sense that the
[municipality] could have prevented the violation with an
appropriate policy.” Gibson, 290 F.3d at 1194.

   The Supreme Court has explained that these heightened
requirements for establishing responsibility for a policy of
omission are necessary to avoid imposing respondeat superior
liability, which would run afoul of Monell. See Bd. of Cnty.
Comm’rs v. Brown, 520 U.S. 397, 403-04 (1997). After all,
when a municipal employee commits a constitutional tort, it
could always be alleged that the municipality failed to enact
a policy that would have prevented the tort. Without the rigor-
ous state of mind requirements set out in Canton and subse-
quent cases, there would be nothing left of Monell’s rule
against respondeat superior liability. See Connick v. Thomp-
son, 131 S. Ct. 1350, 1359-60 (2011); Bd. of Cnty. Comm’rs,
520 U.S. at 406-07. Canton’s standards thus ensure that, even
if the alleged defect in the municipality’s policy is one of
omission, the acts of constitutional tortfeasors can still “fairly
be said to be those of the municipality.” Bd. of Cnty.
Comm’rs, 520 U.S. at 404.

   As the Supreme Court has also observed, however, such
concerns are not present “[w]here a plaintiff claims that a par-
ticular municipal action itself violates federal law, or directs
an employee to do so.” Id. Under this “direct path” to munici-
pal liability, a plaintiff must “prove that the municipality
acted with ‘the state of mind required to prove the underlying
violation,’ just as a plaintiff does when he or she alleges that
a natural person has violated his federal rights.” Gibson, 290
F.3d at 1185 (quoting Bd. of Cnty. Comm’rs, 520 U.S. at 405).

   [11] As Tsao has stated her claim, the alleged deficiency
is properly seen as one of omission. Desert Palace in effect
adopted two policies, with a gap between them that created
the circumstances in which Tsao was arrested. First, Desert
Palace keeps records of those it ejects from its casinos, and
when those people return, it arrests them for trespassing or
                    TSAO v. DESERT PALACE, INC.                 12869
issues them citations under the SILA program. Second, Desert
Palace sends promotional offers to repeat customers inviting
them to visit the casino. Desert Palace’s security staff has no
way of determining whether someone they are about to arrest
for trespassing has in fact been invited onto the property, and
the marketing staff apparently is not informed that someone
has been warned never to return. Desert Palace conducts these
two functions entirely separately, without any safeguard in
place to prevent the situation that arose here. If any patron
evicted by the security department were automatically
removed from the marketing department’s mailing list, for
instance, Tsao would not have received invitations, and there
would be no question that she was trespassing. It is this gap
in communication between the two departments, this omis-
sion, that led to the alleged constitutional violation in this
case.

   A review of our case law on policies of commission further
supports the idea that, as Tsao has stated her claim, the policy
at issue here is one of omission. An official municipal policy,
the Court has explained, “includes the decisions of a govern-
ment’s lawmakers, the acts of its policymaking officials, and
practices so persistent and widespread as to practically have
the force of law.” Connick, 131 S.Ct. at 1359. Thus under the
“direct path” to municipal liability, a policy may be facially
unconstitutional, like “a city’s policy of discriminating against
pregnant women in violation of the Fourteenth Amendment.”
Gibson, 290 F.3d at 1185 (citing Monell, 436 U.S. at 658). Or
the constitutional violation may be the result of a direct order
from a policymaking official, like “a policy-maker’s order to
its employees to serve capiases15 in violation of the Fourth
Amendment.” Id. at 1185-86 (citing Pembaur v. City of Cin-
cinnati, 475 U.S. 469 (1986)). There is no suggestion here
  15
     “A capias is a writ of attachment commanding a county official to
bring a subpoenaed witness who has failed to appear before the court to
testify and to answer for civil contempt.” Gibson, 290 F.3d at 1185 n.6
(quoting Pembaur, 475 U.S. at 472 n.1).
12870                 TSAO v. DESERT PALACE, INC.
that Desert Palace’s overall policy is to oust unwanted gam-
blers even though they have been invited onto the property,
that there is any such persistent or widespread practice, or that
a policymaking official directed Makeley to arrest her
although the policymaker knew that she was at the casino by
invitation.16

   [12] As Tsao has stated her claim, the cause of her arrest
is thus best seen as an omission in Desert Palace’s policies—
the failure to create a coordination system between security
and marketing. Tsao therefore must show “that [Desert Pal-
ace’s] deliberate indifference led to [this] omission.” Gibson,
290 F.3d at 1186.

   [13] To show deliberate indifference, Tsao must demon-
strate “that [Desert Palace] was on actual or constructive
notice that its omission would likely result in a constitutional
violation.” Id. (citing Farmer, 511 U.S. at 841). Only then
does the omission become “the functional equivalent of a
decision by [Desert Palace] itself to violate the Constitution.”
Connick, 131 S. Ct. at 1360. As we observed in Gibson,
“[p]olicies of omission regarding the supervision of employ-
ees . . . can be ‘policies’ or ‘customs’ that create municipal
liability . . . only if the omission ‘reflects a deliberate or con-
scious choice’ to countenance the possibility of a constitu-
tional violation.” 290 F.3d at 1194 (quoting Canton, 489 U.S.
at 389-90) (internal quotation marks omitted).

   Tsao has not alleged that Desert Palace had actual notice of
the flaw in its policies. The question thus becomes whether
the risk that security personnel might arrest someone who had
  16
    Makeley did consult with John Banner, the casino manager, before
approaching Tsao. But when asked whether Banner had instructed him to
arrest her if she didn’t have identification, Makeley insisted that “that call
was mine.” Moreover, there is no indication that Banner knew, or was in
a position to know, that Tsao had received promotional invitations cover-
ing the period in question.
                  TSAO v. DESERT PALACE, INC.              12871
been invited to the casino was so “obvious” that ignoring it
amounted to deliberate indifference.

   [14] Tsao has not introduced facts sufficient to make this
showing. First, there is no indication that this problem has
ever arisen other than in the case of Tsao herself. In consider-
ing claims based on a failure to train municipal employees,
the Court has noted that “a pattern of similar constitutional
violations by untrained employees is ‘ordinarily necessary’ to
demonstrate deliberate indifference.” Connick, 131 S. Ct. at
1360 (quoting Bd. of Cnty. Comm’rs, 520 U.S. at 409). Simi-
larly, the absence here of any evidence of a pattern makes it
far less likely that Tsao can prove Desert Palace was “on
actual or constructive notice,” Farmer, 511 U.S. at 841 (quot-
ing Canton, 489 U.S. at 396) (internal quotation marks omit-
ted), that its policy would lead to constitutional violations.

   [15] Second, it is far from obvious that the omissions in
Desert Palace’s policies would necessarily give rise to this sit-
uation. Tsao is a professional gambler, and, having been
kicked out of the casino at least five times under a variety of
aliases, was well aware that she was most likely not welcome
at the Caesars Palace blackjack tables. For the situation at the
heart of this case to arise, two circumstances must coalesce:
First, someone like Tsao—who knows that she is persona non
grata as far as the casino is concerned—would have to give
the casino her real name and address at some point, so they
would appear on the marketing department’s mailing list for
promotional offers. Second, the unwanted gambler would
have to interpret those promotional offers as invitations over-
riding previous trespass warnings and decide to return to the
casino. It is not “obvious” that both of these things will hap-
pen, and Tsao has not introduced any evidence suggesting that
Desert Palace was on constructive notice that its policy’s
omissions made this situation likely.

   Under Monell, a plaintiff must also show that the policy at
issue was the “actionable cause” of the constitutional viola-
12872             TSAO v. DESERT PALACE, INC.
tion, which requires showing both but-for and proximate cau-
sation. Harper, 533 F.3d at 1026. We are not convinced that
the casino’s omission was the but-for cause of Tsao’s alleg-
edly unlawful arrest. Even if marketing had told the security
department that it sent Laurie Tsao an invitation, Makeley had
no way at the outset of connecting the woman whose name
was on the invitation with the woman he saw at the blackjack
table. After all, Makeley had a record that she was ejected
under the name Shuyu Deng; she was using a player’s card
with the name Monica Lieu; she gave her name Laurie Chang;
and she was not carrying identification. Makeley did not learn
the name was Laurie Tsao until after he had detained her,
handcuffed her, taken her to the interrogation room, and kept
her there for some time.

  [16] For the foregoing reasons, we affirm the District
Court’s grant of summary judgment as to Tsao’s § 1983 claim
against Desert Palace.

  B.    Officer Crumrine

   Tsao’s § 1983 claim against Crumrine is relatively straight-
forward. The dispositive question is whether Crumrine had
probable cause to arrest Tsao for obstructing his investigation,
in violation of NRS § 197.190. The facts are undisputed, so
the existence of probable cause is a question of law. See Peng
v. Mei Chin Penghu, 335 F.3d 970, 979-80 (9th Cir. 2003);
Act Up!/ Portland v. Bagley, 988 F.2d 868, 873 (9th Cir.
1993). The District Court held as a matter of law that Crum-
rine had probable cause to think that Tsao was obstructing his
investigation. We agree.

  In his Declaration of Arrest, Crumrine stated:

    Due to the fact that Tsao gave a different last name
    than the one she is registered to DMV with, the only
    legal name that I could access to verify Tsao’s iden-
    tity, I placed Tsao under arrest for Providing False
                  TSAO v. DESERT PALACE, INC.             12873
    Information to a Police Officer NRS 197.190 and
    transported Tsao to Clark County Detention Center
    where she was booked accordingly.

Section 197.190 of the Nevada Revised Statutes, “Obstructing
public officer,” states in its entirety:

    Every person who, after due notice, shall refuse or
    neglect to make or furnish any statement, report or
    information lawfully required of him by any public
    officer, or who, in such statement, report or informa-
    tion shall make any willfully untrue, misleading or
    exaggerated statement, or who shall willfully hinder,
    delay or obstruct any public officer in the discharge
    of his official powers or duties, shall, where no other
    provision of law applies, be guilty of a misdemeanor.

According to Crumrine, he arrested Tsao for violating that
part of NRS § 197.190 that punishes the making of “any will-
fully untrue . . . statement” to a “public officer” after “due
notice,” assuming that the information requested was “law-
fully required” of the individual.

   Under NRS § 171.123, police officers may detain individu-
als reasonably suspected of criminal behavior in order “to
ascertain the person’s identity and the suspicious circum-
stances.” NRS § 171.123(3). The same statute provides that a
person so detained “shall identify himself or herself, but may
not be compelled to answer any other inquiry of any peace
officer.” Id. Hiibel v. Sixth Judicial District Court of Nevada,
542 U.S. 177, 190-91 (2004) upheld NRS § 171.123’s
requirement that a suspect identify herself to a police officer
against several constitutional challenges.

   [17] The only question, then, is whether Crumrine had
probable cause to believe that Tsao was obstructing his inves-
tigation in violation of NRS § 197.190. Notably, we need not
confine our inquiry to Crumrine’s declaration of arrest, which
12874             TSAO v. DESERT PALACE, INC.
said that Tsao was being arrested for “providing false infor-
mation to a police officer”; the question is whether Crumrine
had probable cause to arrest Tsao for any offense. Devenpeck
v. Alford, 543 U.S. 146, 152-54 (2004) (noting that an offi-
cer’s “subjective reason for making the arrest need not be the
criminal offense as to which the known facts provide probable
cause”). We hold that he did.

   Probable cause exists if Crumrine knew “reasonably trust-
worthy information sufficient to warrant a prudent person in
believing that [Tsao] had committed or was committing an
offense.” Arpin v. Santa Clara Valley Transp. Agency, 261
F.3d 912, 924-25 (9th Cir. 2001) (quoting Allen v. City of
Portland, 73 F.3d 232, 236 (9th Cir. 1995)) (internal quota-
tion marks omitted). While an officer may not ignore exculpa-
tory evidence that would negate a finding of probable cause,
“ ‘[o]nce probable cause is established, an officer is under no
duty to investigate further or to look for additional evidence
which may exculpate the accused.’ ” Broam v. Bogan, 320
F.3d 1023, 1032 (9th Cir. 2003) (alteration in original) (quot-
ing Ahlers v. Schebil, 188 F.3d 365, 371 (6th Cir. 1999)).

   [18] Crumrine had probable cause to believe that Tsao was
willfully delaying his investigation in violation of the statute
by refusing to provide a name through which her identity as
the person previously “trespassed” could be confirmed or dis-
proved. Tsao was not lying when she gave her married name,
Chang, which does appear on her passport. But by doing so,
she did impede her arrest for trespass for some time, while
Desert Palace security and police looked for her car and
checked her other identifying information. And her motives
for doing so were clearly suspect. In her deposition, Tsao
admitted that she did not want the casino to know that her
name was Tsao, because “that was the most pertinent name”
and because she had had trouble with it at another casino. She
also knew that Tsao was the name on her driver’s license,
bank accounts, credit cards, and Social Security card, so that
withholding that name might make it harder to connect her to
                  TSAO v. DESERT PALACE, INC.             12875
the previously trespassed person. As it happened, Crumrine
soon learned that Tsao’s car was in the casino parking lot
through the use of the panic button on her keys, and was able
to pull up DMV records using the license plate. The discon-
nect between Tsao’s insistence that her name was Chang and
the records associated with her license plate and Social Secur-
ity numbers gave Crumrine probable cause to believe she had
been obstructing his investigation. She made a statement
regarding her name that was misleading and calculated to
delay the discovery of her identity, even though the name
given was not literally false.

   Tsao relies on Arpin for the proposition that Crumrine’s
duty to investigate included a duty to allow her to explain her-
self before being arrested. In Arpin, however, an officer
arrested a bus passenger without performing any independent
investigation whatsoever, relying entirely on the bus driver’s
report that the passenger had assaulted him. 261 F.3d at
924-25. The officer, we noted, “refused to identify himself,
would not inform [Arpin] of the reason she was being
arrested, and did not allow Arpin to explain her side of the
story prior to arresting her.” Id. at 925. Probable cause for
Crumrine’s belief that Tsao had committed a crime, by con-
trast, was not based on the report of a third party; it arose
from the very investigation Crumrine performed. Unlike
Arpin, Tsao was given an opportunity to answer questions and
explain the situation. It was Tsao’s obfuscatory answers to
Crumrine’s simple questions that created probable cause to
arrest her. Tsao had many opportunities to tell Crumrine the
name she had every reason to know—and indeed indicated
that she did know—was the one he wanted for his investiga-
tion. Crumrine had probable cause to believe that Tsao had
delayed his investigation with her misleading response. That
Crumrine later learned that Tsao and Chang were the same
person did not destroy probable cause for an arrest based on
her earlier violation of the statute.

  [19] We therefore affirm the District Court’s grant of sum-
mary judgment to Crumrine on Tsao’s § 1983 claim.
12876             TSAO v. DESERT PALACE, INC.
II.   State law claims

   [20] In addition to her § 1983 claims, Tsao alleged a num-
ber of claims arising under the common law of Nevada
against both defendants. We affirm the District Court’s grant
of summary judgment to Desert Palace on the abuse of pro-
cess claim for the reason the District Court gave: Tsao failed
to adduce any evidence that Desert Palace acted with “an ulte-
rior purpose.” LaMantia v. Redisi, 38 P.3d 877, 879 (Nev.
2002).

   [21] For most of the other common law claims, the District
Court’s determination that Makeley and Crumrine each had
probable cause to arrest Tsao formed the basis for the sum-
mary judgment to the respective defendants. Because we con-
clude that Crumrine did have probable cause to arrest Tsao,
we affirm the grant of summary judgment to Crumrine on the
battery, false imprisonment, and defamation claims. We
vacate, however, the grant of summary judgment as to the bat-
tery, false imprisonment, assault, and premises liability claims
directed at Desert Palace. We now remand those claims to the
District Court for further proceedings, for reasons we shall
explain shortly.

   Before doing so, we note that the District Court miscon-
strued Tsao’s final state law claim, alleging that Desert Palace
committed common-law defamation. Under Nevada common
law, defamation requires “(1) a false and defamatory state-
ment of fact by the defendant concerning the plaintiff; (2) an
unprivileged publication to a third person; (3) fault, amount-
ing to at least negligence; and (4) actual or presumed dam-
ages.” Pope v. Motel 6, 114 P.3d 277, 282 (Nev. 2005).
Tsao’s defamation claim is based on K-Mart Corp. v. Wash-
ington, 866 P.2d 274 (Nev. 1993) (per curiam), in which the
plaintiff was handcuffed and marched through a store on sus-
picion of shoplifting. Id. at 281. The Nevada Supreme Court
held that “[t]he imputation of shoplifting, by words or by pan-
                      TSAO v. DESERT PALACE, INC.                     12877
tomime, if communicated to a third party, is unquestionably
slander per se.” Id. at 283.

   [22] The District Court apparently believed that Tsao’s
defamation claim against Desert Palace was based on Make-
ley’s communication to Crumrine that Tsao had trespassed.
On that understanding, the District Court held the communi-
cation privileged, as communications to police before the
instigation of criminal proceedings are protected by a quali-
fied privilege. See Pope, 114 P.3d at 284. But Tsao’s defama-
tion claim is not premised on any communications to
Crumrine. Instead, it is grounded on Makeley’s act of escort-
ing her off the casino floor in handcuffs in view of other
patrons. The qualified privilege does not apply in such cir-
cumstances. See id.; K-Mart, 866 P.2d at 282. We therefore
vacate the District Court’s grant of summary judgment to
Desert Palace on Tsao’s defamation claim, with the observa-
tion that this claim too will turn on whether there was in fact
probable cause to detain Tsao—which, in turn, depends on the
legal effect of the promotional offers under state law.17

   As all the federal law claims have now been resolved with-
out reaching the probable cause question, the circumstances
under which the District Court decided to exercise its discre-
tionary supplemental jurisdiction over the state law claims has
changed. See Carnegie-Mellon Univ. v. Cohill, 484 U.S. 343,
345, 357 (1988) (district court has discretion “to remand a
properly removed case to state court when all federal-law
claims in the action have been eliminated and only pendent
  17
     We note that with respect to Tsao’s battery claim, the Nevada
Supreme Court has held that “a private person, when arresting another per-
son pursuant to [the Nevada Citizen’s Arrest Statute], may use no more
force than is necessary and reasonable to secure the arrest.” State v. Wen-
dell, 118 Nev. 206, 209 (Nev. 2002) (en banc). Here, although Tsao did
not behave belligerently, Makeley and two other security guards placed
her in handcuffs and led her to the interview room. It is possible, therefore,
that Makeley’s conduct may not qualify as battery regardless of the proba-
ble cause determination.
12878              TSAO v. DESERT PALACE, INC.
state-law claims remain” when doing so “serves the principles
of economy, convenience, fairness, and comity”). We there-
fore remand those claims to the District Court for reconsidera-
tion of the supplemental jurisdiction determination.

   In doing so, we note in particular that we have now dis-
posed of “all claims over which [the District Court] has origi-
nal jurisdiction,” 28 U.S.C. § 1367(c)(3), without reaching the
probable cause question that overlaps with the state law
claims. Moreover, the remaining state law claims “raise[ sev-
eral] novel or complex issue[s] of State law” not recognized
by the District Court Id. § 1367(c)(1).

   Of particular difficulty is the question whether the promo-
tional offers Tsao received were legally sufficient to rescind
the prior trespass notice. Nevada’s trespass statute does not
address the manner in which a trespass warning may be
rescinded, see NRS § 207.200, and there is no Nevada case
law dealing with the issues of consent involved here. Desert
Palace does not seriously dispute the conclusion that Tsao
could have permissibly stayed at the Caesars Palace hotel, bet
on basketball at its casino, or taken advantage of any of the
other offers it mailed her. It argues, instead, that its invitations
to Tsao were limited to those activities, pointing out that “[t]o
be effective, consent must be . . . to the particular conduct, or
substantially the same conduct.” Restatement (Second) of
Torts § 892A(2)(b). The Restatement also specifies that the
precise scope of the consent is “normally for the trier of fact
to determine,” id. § 892A cmt. d. In making that determina-
tion, it is proper to take into account the consequences that
Desert Palace subjectively anticipates when it sends these
sorts of offers, as well as the consequences that were reason-
ably foreseeable to it. See id. § 892A cmts. d & e; see also
Shaheen v. Riviera Hotel Corp., 347 P.2d 285, 287 (Nev.
1959); Babcock & Wilcox Co. v. Nolton, 71 P.2d 1051, 1053
(Nev. 1937).
                     TSAO v. DESERT PALACE, INC.                     12879
   The fact that Tsao may not have subjectively believed that
she had been invited to play blackjack at Caesars Palace
might well have no legal significance. Consent can be effec-
tive when the actor, unaware that consent has been given,
intends to trespass. See Restatement (Second) of Torts § 892,
Illustration 1.18 Thus, it could be pertinent—depending on
what Nevada law concerning consent to trespass turns out to
be—whether Desert Palace anticipated that those potential
customers invited to stay at its hotel or bet on basketball
would gamble in its casino.

   A second novel state law question arises from Tsao’s sug-
gestion that even if Desert Palace had probable cause to
believe she was trespassing, probable cause is not a defense
to a claim of false imprisonment where there is a citizen’s
arrest, as Nevada’s citizen’s arrest statute authorizes citizen’s
arrests for misdemeanors only when a crime has in fact been
committed. See NRS § 171.126 (“A private person may arrest
another: . . . For a public offense committed or attempted in
the person’s presence.”); cf. Atwater v. City of Lago Vista,
532 U.S. 318, 352 (2001) (“It is of course easier to devise a
minor-offense limitation by statute . . . . It is, in fact, only nat-
ural that States should resort to this sort of legislative regula-
tion, for . . . it is in the interest of the police to limit petty-
offense arrests . . . .”). Tsao’s position is consistent with the
general common law rule, see Roth v. Golden Nugget Casi-
no/Hotel, Inc., 576 F. Supp. 262, 266 (D. N.J. 1983) (citing
Prosser on Torts § 17 at 100 (1971)), but there is no Nevada
precedent on the question, it appears. There thus may be no
  18
     That is not to say that an actor’s subjective beliefs are always irrele-
vant. For example, in a civil case, “an overt manifestation of assent or
willingness would not be effective [as consent] . . . if the [invitee] knew,
or probably if he ought to have known in the exercise of reasonable care,
that the [landowner] was mistaken as to the nature and quality of the inva-
sion intended.” Theofel v. Farey-Jones, 359 F.3d 1066, 1073 (9th Cir.
2004) (quoting Prosser & Keeton on the Law of Torts § 18, at 119 (W.
Page Keeton ed., 5th ed. 1984)).
12880             TSAO v. DESERT PALACE, INC.
way to resolve Tsao’s state law false arrest claim without first
determining another undecided question of state law.

   Were we required to address these trespass-related issues to
dispose of this case in its current posture, we would certify
them to the Nevada Supreme Court, as they are potentially
weighty and unsettled questions of state law. But our disposi-
tion of the federal claims has not required us to decide
whether Desert Palace had probable cause to arrest Tsao for
trespassing. The District Court’s decision to exercise its dis-
cretion to assert jurisdiction over the state law issues assumed
its resolution of the probable cause issue in the federal law
analysis. As the District Court’s probable cause analysis did
not take account of the complexities just noted, as well as the
actual nature of the defamation claim, we remand for the Dis-
trict Court to reconsider its assertion of jurisdiction over the
state law claims. If it decides to consider those claims, then
the District Court should reevaluate its rulings in light of this
opinion.

III.    Conclusion

   [23] In sum, we affirm the grant of summary judgment to
Desert Palace on Tsao’s § 1983 and abuse of process claims;
affirm the grant of summary judgment to Crumrine on Tsao’s
§ 1983, common law false arrest, battery, and defamation
claims; vacate the grant of summary judgment on all other
claims; and remand for further proceedings. We also vacate
the award of attorneys’ fees to Crumrine and the award of
costs to both defendants, as “[a] prevailing defendant is enti-
tled to attorney fees under 42 U.S.C. § 1988 only when the
plaintiff’s claims are ‘groundless, without foundation, frivo-
lous, or unreasonable.’ ” Karam v. City of Burbank, 352 F.3d
1188, 1195 (9th Cir. 2003) (citation omitted). Tsao’s § 1983
claims do not meet this standard, for the reasons we have indi-
cated.

 AFFIRMED IN PART, VACATED IN PART, AND
REMANDED.
