                  FOR PUBLICATION
  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT

JOY BLACK SUMMERS, as Personal         
Representative of the Estate of
Betty Jane Black, deceased,
 Plaintiff-Appellant/Cross-Appellee,       Nos. 05-35220
                  v.                            05-35268
DELTA AIR LINES, INC., and
SKYWEST AIRLINES, INC.,                        D.C. No.
                                             CV-03-00134-
       Defendants-Appellees/Cross-                LBE
                         Appellants,            OPINION
                 and
DOES 20,
                        Defendants.
                                       
       Appeal from the United States District Court
                for the District of Montana
       Leif B. Erickson, Magistrate Judge, Presiding

                  Argued and Submitted
          February 7, 2007—Seattle, Washington

                 Filed November 27, 2007

       Before: Susan P. Graber, Richard A. Paez, and
               Carlos T. Bea, Circuit Judges.

                  Opinion by Judge Graber




                            15187
              SUMMERS v. DELTA AIR LINES, INC.      15189


                        COUNSEL

Dane J. Durham, Sebastopol, California, for the plaintiff-
appellant/cross-appellee.
15190          SUMMERS v. DELTA AIR LINES, INC.
Mark S. Williams, Williams Law Firm, P.C., Missoula, Mon-
tana, for the defendants-appellees/cross-appellants.


                           OPINION

GRABER, Circuit Judge:

   Betty Jane Black disembarked from a SkyWest Airlines air-
plane, slipped and fell, and suffered injuries that allegedly led
to her death. Plaintiff Joy Black Summers, Mrs. Black’s
daughter-in-law and the personal representative of her estate,
brought suit against Defendants Delta Airlines and SkyWest
Airlines, alleging that Defendants negligently failed to pro-
vide wheelchair assistance to Mrs. Black. Trial commenced
but, before Plaintiff completed her case-in-chief, the district
court granted judgment as a matter of law to Defendants on
all claims. On appeal, we examine two procedural require-
ments in Federal Rule of Civil Procedure 50(a): that, before
the district court may grant judgment as a matter of law, (1)
the moving party must specify “the judgment sought and the
law and the facts” forming the grounds for its motion and (2)
the nonmoving party must be “fully heard” on those grounds.

        FACTUAL AND PROCEDURAL HISTORY

   In late 2002, Decedent Betty Jane Black, aged 78 and trav-
eling alone, flew round-trip from Missoula, Montana, to
Atlanta, Georgia, on flights jointly operated by Defendant air-
lines. Her itinerary included plane changes in Salt Lake City,
Utah, both on her initial trip to Atlanta and on her return flight
to Missoula. A relative had bought Decedent’s ticket and
requested wheelchair assistance. Defendants provided wheel-
chair assistance on the first three legs of the trip. On the last
leg of the trip, however, the flight crew departing from Salt
Lake City erroneously believed that no passenger required
wheelchair assistance, and they so informed their counterparts
at the Missoula airport.
                 SUMMERS v. DELTA AIR LINES, INC.                 15191
   Upon arrival in Missoula, Decedent eventually left the air-
craft on foot and began walking up the jetway,1 an extendable
enclosed ramp leading from the terminal to the door of the
aircraft that facilitates the movement of passengers to and
from the aircraft. Partway up the ramp of the jetway, Dece-
dent either tripped or slipped on a metal ledge, fell backward,
and struck her head on a jagged piece of metal. Her fall
resulted in a mild concussion and a 3-centimeter gash on her
head, which bled profusely. She was taken to a hospital,
treated, and released. On January 27, 2003, nearly three
months after her fall, Decedent died, allegedly due to compli-
cations arising from the injuries suffered in the fall.

   Plaintiff sued in state court, and Defendants removed the
case to federal court on the basis of diversity jurisdiction. 28
U.S.C. §§ 1332, 1441(a). A jury trial began on Monday,
December 13, 2004, and was scheduled to last at least one
week. By agreement of the parties and with the consent of the
district court, one of Plaintiff’s key lay liability witnesses, Dr.
William Doyle, was set to testify late in the week, on Friday,
December 17, to accommodate his schedule. Dr. Doyle, a fel-
low passenger on the plane who also happens to be an emer-
gency room physician, was standing only a few feet away
from Decedent when she fell.

   On the second day of trial, Tuesday, December 14, Defen-
dants moved for judgment as a matter of law, citing two spe-
cific deficits in Plaintiff’s case-in-chief. Plaintiff opposed the
motion and filed a brief the next morning, on Wednesday,
December 15, contesting the two issues raised by Defendants’
motion. Early in the afternoon of the same day, the district
  1
    A disputed fact at trial was whether, and to what extent, Decedent
waited for a wheelchair. Another disputed fact was whether a wheelchair
was present in the jetway. In reviewing a grant of judgment as a matter
of law, we must view the evidence in the light most favorable to the non-
moving party, and we must draw all reasonable inferences in favor of that
party. Reeves v. Sanderson Plumbing Prods., Inc., 530 U.S. 133, 149-50
(2000).
15192          SUMMERS v. DELTA AIR LINES, INC.
court asked for an offer of proof from Plaintiff’s lawyer as to
what the remaining liability witnesses would say. Plaintiff’s
lawyer replied that he had telephoned Dr. Doyle during the
lunch break, and the lawyer relayed the content of that con-
versation.

  After a five-minute recess, the district court granted judg-
ment as a matter of law to Defendants. The legal bases for the
decision, however, were different from those raised in Defen-
dants’ motion. Plaintiff immediately objected, but the district
court stood by its ruling.

   The next week, Plaintiff filed a motion for a new trial pur-
suant to Federal Rule of Civil Procedure 59. The district court
denied the motion for a new trial in a written order. In that
order, the district court reaffirmed its earlier ruling but added
one of the arguments in Defendants’ motion as an additional
basis for the grant of judgment as a matter of law. Plaintiff
timely appealed, and Defendants cross-appealed on an eviden-
tiary issue.

                 STANDARDS OF REVIEW

   We review de novo a district court’s grant of judgment as
a matter of law. McSherry v. City of Long Beach, 423 F.3d
1015, 1019 (9th Cir. 2005). We review for abuse of discretion
the district court’s decision to admit expert testimony. Kumho
Tire Co. v. Carmichael, 526 U.S. 137, 152 (1999).

                        DISCUSSION

  A.    Judgment as a Matter of Law

  The district court’s grant of judgment to Defendants as a
matter of law before the close of Plaintiff’s case-in-chief
requires us to examine the procedural requirements of Federal
Rule of Civil Procedure 50(a). In particular, we must deter-
mine (1) whether the court erred by granting judgment as a
                  SUMMERS v. DELTA AIR LINES, INC.                  15193
matter of law on grounds not raised in Defendants’ motion,
and (2) whether the court erred by requiring Plaintiff to make
an offer of proof instead of introducing the live testimony of
a key liability witness.

   [1] Rule 50(a) reads in full:

         (1) If during a trial by jury a party has been fully
      heard on an issue and there is no legally sufficient
      evidentiary basis for a reasonable jury to find for the
      party on that issue, the court may determine the issue
      against that party and may grant a motion for judg-
      ment as a matter of law against that party with
      respect to a claim or defense that cannot under the
      controlling law be maintained or defeated without a
      favorable finding on that issue.

         (2) Motions for judgment as a matter of law may
      be made at any time before submission of the case
      to the jury. Such a motion shall specify the judgment
      sought and the law and the facts on which the mov-
      ing party is entitled to the judgment.

Fed. R. Civ. P. 50(a) (2004) (amended 2006) (emphases
added).2 Rule 50(a) thus allows a court to remove “issue[s]"—
claims, defenses, or entire cases—from the jury when there is
no “legally sufficient evidentiary basis” to support a particular
outcome. Id. But the Rule prescribes certain procedures: A
party must be “fully heard” before the court may grant judg-
ment as a matter of law, Fed. R. Civ. P. 50(a)(1), and a
motion must “specify the judgment sought and the law and
  2
    The quoted version of the Rule was in effect during the trial. We note
that the Rule recently was amended, but the amendments were “intended
to be stylistic only.” Fed. R. Civ. P. 50 advisory committee’s note to 2006
amendment.
15194               SUMMERS v. DELTA AIR LINES, INC.
the facts on which the moving party is entitled to the judg-
ment,” Fed. R. Civ. P. 50(a)(2).3

   The advisory committee note, which “guides our interpreta-
tion of Rule 50,” Waters v. Young, 100 F.3d 1437, 1441 (9th
Cir. 1996), explains that Rule 50(a)(1)

       authorizes the court to consider a motion for judg-
       ment as a matter of law as soon as a party has com-
       pleted a presentation on a fact essential to that
       party’s case. Such early action is appropriate when
       economy and expedition will be served. In no event,
       however, should the court enter judgment against a
       party who has not been apprised of the materiality of
       the dispositive fact and been afforded an opportunity
       to present any available evidence bearing on that
       fact.

Fed. R. Civ. P. 50 advisory committee’s note to 1991 amend-
ments. Additionally, the requirement that the motion “specify
the judgment sought and the law and the facts on which the
moving party is entitled to the judgment,” Fed. R. Civ. P.
50(a)(2), allows the responding party an opportunity “to cor-
rect any overlooked deficiencies in the proof.” Fed. R. Civ. P.
50 advisory committee’s note to 1991 amendments.

  In essence, the machinery of Rule 50(a) operates to achieve
a balance between competing, desirable goals. On the one
hand, “economy and expedition” are served by cutting short
  3
   Defendants argue that a literal reading of the text of Rule 50(a)(2)
means that the district court may grant a motion “at any time,” even if the
nonmoving party has not been “fully heard” as required by Rule 50(a)(1).
This argument is foreclosed by McSherry, 423 F.3d at 1019:
      [Rule 50(a)(2)] supplements [Rule 50(a)(1)] by instructing the
      moving party that it may file a motion until the case is submitted
      to the jury, but does not eliminate the substantive requirement
      that a party be “fully heard” on an issue prior to the grant of judg-
      ment as a matter of law.
               SUMMERS v. DELTA AIR LINES, INC.            15195
trials containing legally insufficient evidence “as soon as it is
apparent that [a] party is unable to carry a burden of proof that
is essential to that party’s case.” Id. On the other hand, the
procedural requirements that, before a motion may be granted,
a party must be “fully heard on an issue” and be given an
opportunity to correct any deficiencies assure fairness to the
parties and promote the trial court’s fact-finding role. See gen-
erally Lifshitz v. Walter Drake & Sons, Inc., 806 F.2d 1426,
1428-29 (9th Cir. 1986) (describing the “important purposes”
of Rule 50(a)).

  1. The District Court’s Original Grant of Judgment as a
  Matter of Law

   Defendants’ motion for judgment as a matter of law rested
on two legal grounds—proximate cause and the defectiveness
of the jetway—and therefore complied with Rule 50(a)’s
requirement that the motion “specify the judgment sought and
the law and the facts” underlying the motion. Understandably,
and as envisioned by Rule 50(a), Plaintiff limited her brief in
opposition, her last-minute telephone conversation with Dr.
Doyle, her offer of proof, and her oral argument to the two
grounds raised in Defendants’ motion. Ruling from the bench,
though, the district court granted judgment as a matter of law
on three legal bases not raised in Defendants’ motion and not
otherwise previewed to Plaintiff—breach of duty, compara-
tive fault, and breach of contract. Plaintiff’s lawyer immedi-
ately objected that “there was no motion made on this legal
basis.” The court responded, “[w]ell, if I expanded the motion
beyond its scope, mea culpa. But I still stand by that ruling.”
It is therefore clear from the record that Plaintiff never was
given an opportunity to address—either with evidence or with
arguments—the legal bases for the district court’s ruling.

   [2] A party who has been called on to respond to a Rule
50(a) motion must have a meaningful opportunity to reply and
must not be sandbagged by a decision on grounds not prop-
erly noticed. In Waters, we reversed the district court’s grant
15196          SUMMERS v. DELTA AIR LINES, INC.
of judgment as a matter of law to the defendant immediately
following the close of the plaintiff’s case, because the court
had neither explained the basis for its ruling nor given the
plaintiff an opportunity to cure any deficiencies. 100 F.3d at
1441. We held that “Federal Rule of Civil Procedure 50
requires district courts to apprise parties of the deficiencies in
their proof, and to give them an opportunity to present further
evidence on the dispositive facts, before granting judgment as
a matter of law against them.” Id. at 1442; accord Teneyck v.
Omni Soreham Hotel, 365 F.3d 1139, 1149 (D.C. Cir. 2004).
Although the district court in this case gave Plaintiff an
opportunity to address the matters raised in Defendants’
motion, “that ‘opportunity’ [wa]s rendered meaningless,”
Waters, 100 F.3d at 1441, when the court granted the motion
on wholly different grounds. Plaintiff was neither apprised of
the alleged deficiencies in her proof nor given the opportunity
to cure such deficiencies. We therefore hold that the district
court erred in granting judgment as a matter of law to Defen-
dants on legal bases neither raised in Defendants’ motion nor
otherwise previewed to Plaintiff by the district court.

  2.    The District Court’s Amended Ruling

   In its written order denying Plaintiff’s motion for a new
trial, the district court amended its grant of judgment as a mat-
ter of law to include the issue of proximate cause—one of the
arguments raised in Defendants’ motion and addressed by
Plaintiff. Before we can reach the merits of whether the dis-
trict court properly granted judgment as a matter of law on the
basis of proximate cause, however, we first must address
whether the record is adequate for appellate review and, more
specifically, whether the method of proof required by the dis-
trict court in this case—an offer of proof—is permissible in
light of Rule 50(a)’s requirement that a party be “fully heard.”

   By prior agreement of the parties and with the consent of
the district court, Dr. Doyle was scheduled to testify on Fri-
day, December 17, 2004. On Wednesday morning, however,
                  SUMMERS v. DELTA AIR LINES, INC.                  15197
the district court expressed a desire to rule on Defendants’
motion for judgment as a matter of law. Plaintiff’s lawyer was
able to telephone Dr. Doyle during the lunch break and, on
the instruction of the district court, relayed the gist of the con-
versation as an offer of proof as to Dr. Doyle’s anticipated
testimony. But the court precluded Plaintiff from eliciting Dr.
Doyle’s testimony live, before the jury. We hold that the
court, in so doing, violated the requirement that a party be
“fully heard” before a judgment as a matter of law may be
granted.

   [3] As the advisory committee’s note makes clear, Rule
50(a)(1) “authorizes the court to consider a motion for judg-
ment as a matter of law as soon as a party has completed a
presentation on a fact essential to that party’s case.” Fed. R.
Civ. P. 50 advisory committee’s note to 1991 amendments
(emphasis added). Once trial has begun, the presentation of a
party’s case is generally achieved—unless a fact is stipulated
—through evidentiary exhibits and live testimony, not
through offers of proof. Plaintiff had not completed her pre-
sentation on any of the essential disputed facts because Dr.
Doyle, a percipient witness on liability, had not testified yet.
Dr. Doyle was on the same flight as Decedent and stood only
a few feet away from her when she fell in the jetway. He
therefore was in a position to testify concerning (among other
issues in dispute) the amount of time, if any, Decedent waited
on the plane, the presence or absence of a wheelchair in the
jetway, and the general conditions of the jetway.

   [4] We hold that, when a party seeks during trial to present
relevant and admissible testimony from a witness on a dis-
puted issue, Rule 50(a) precludes the district court from
requiring that the testimony be given through an offer of proof
instead.4 Our holding today parallels a recent ruling by the
  4
   Nothing in our opinion affects the trial court’s authority to require an
offer of proof under Rules 103, 402, and 403 of the Federal Rules of Evi-
dence when ruling on a challenge to the relevance and admissibility of evi-
15198             SUMMERS v. DELTA AIR LINES, INC.
Fifth Circuit. In Echeverria v. Chevron USA Inc., 391 F.3d
607, 609 (5th Cir. 2004), the plaintiff was partway through his
case-in-chief when the district court “questioned Echeverria’s
lawyer about his remaining evidence on liability” and then
indicated his inclination to grant judgment as a matter of law
to the defendants. Id. “The [district] court then gave Echever-
ria’s lawyer a chance to respond and invited him to proffer the
evidence he would have presented.” Id. at 610. Echeverria’s
lawyer did so, but the district court was unconvinced and
granted judgment as a matter of law to the defendants. Id. The
Fifth Circuit reversed, holding that, for purposes of Rule
50(a), an offer of proof is insufficient because “it is essential
that the nonmoving party be permitted to present all of its evi-
dence [on the disputed ‘issue’].” Id. at 612. See also Francis
v. Clark Equip. Co., 993 F.2d 545, 555 (6th Cir. 1993) (“Rule
50(a) contemplates that a ruling will be made on the basis of
the testimony and documents submitted into evidence.”).

   We agree with the Fifth and Sixth Circuits that the require-
ment that a party be “fully heard” not only allows the district
court to make an informed decision, but also allows us to
review the decision. See Echeverria, 391 F.3d at 610-11 (stat-
ing that “the use of ‘proffered’ summaries of the evidence
inhibits [an appellate] [c]ourt’s review of whether a directed
verdict was proper” (internal quotation marks and brackets
omitted)); Francis, 993 F.2d at 555 (“[I]t is impossible for
this court to review whether, when all reasonable inferences
from the evidence are construed in favor of the nonmoving
party, a reasonable juror could find in favor of the nonmoving
party if he is precluded from presenting the evidence he con-
siders relevant.”). Without the testimony and documents on an

dence. Of course, if a proper offer of proof under those Rules unearths no
relevant and admissible evidence on a dispositive issue, there would be
nothing further to be “fully heard,” and a ruling under Rule 50 might then
be proper. But, in this case, Dr. Doyle’s testimony is directly relevant and
clearly admissible. Not surprisingly, no party challenged Dr. Doyle’s testi-
mony under the Rules of Evidence.
                SUMMERS v. DELTA AIR LINES, INC.             15199
essential disputed issue, we cannot make a fully informed
decision as to whether a grant of judgment as a matter of law
would have been appropriate following a party’s presentation
of evidence on that issue.

   Rule 50(a)’s requirement that a party be allowed to com-
plete its presentation on an essential issue is not unduly bur-
densome. When a case proceeds to trial, there are material
issues of fact for a finder of fact to resolve. Rule 50(a) allows
the district court to end the trial if, after a party has introduced
all evidence on a dispositive issue, it becomes apparent never-
theless that the party cannot prevail. The Fifth Circuit’s words
apply with equal force here:

       Ultimately, the district judge may be right about
    the sufficiency of [the plaintiff’s] evidence on [the
    disputed issue], but endorsing a practice of prema-
    turely entering judgment would circumvent Rule
    50’s requirement that a party be fully heard, and
    would require this court to review a [judgment as a
    matter of law] without all of the plaintiff’s evidence.
    Because the purpose of Rule 50 is, in part, to weigh
    the sufficiency of the evidence before the case is
    submitted to the jury, it is essential that the nonmov-
    ing party be permitted to present all of its evidence.
    Rule 50 is intended to shorten and end needless tri-
    als, but that objective can be achieved by simply
    waiting until the plaintiff rests—at least, waiting
    until the plaintiff rests on [the disputed issue].

Echeverria, 391 F.3d at 612 (footnotes omitted).

  [5] The requirement that a party complete its presentation
on a disputed issue does not necessarily mean that the district
court must wait until the party has completed its entire case.
As explained by the advisory committee’s note, the Federal
Rules of Civil Procedure are structured “to encourage the
court to schedule an order of trial that proceeds first with a
15200          SUMMERS v. DELTA AIR LINES, INC.
presentation on an issue that is likely to be dispositive, if such
an issue is identified in the course of pretrial.” Fed. R. Civ.
P. 50 advisory committee’s note to 1991 amendments; see
also Fed. R. Civ. P. 16(c)(13)-(14). Nothing in our opinion
today affects the wide discretion that a district court enjoys to
control the order of proof; we merely require that the usual
method of proof—through live witness testimony—cannot be
foreclosed, at least with respect to a key witness scheduled to
provide relevant and admissible testimony as part of the
party’s case-in-chief on an essential issue. For example,
instead of requesting an offer of proof, the district court could
have required Plaintiff to finish presenting her liability wit-
nesses before proceeding to her damages witnesses. By
requiring an offer of proof, however, the district court’s grant
of judgment as a matter of law under Rule 50(a) ran afoul of
the requirement that Plaintiff be “fully heard,” because Plain-
tiff had not completed her presentation of relevant and admis-
sible evidence on a dispositive issue. We therefore must
reverse and remand for a new trial.

  B.    Cross-Appeal

   Defendants have cross-appealed, arguing that the district
court should not have permitted Dr. Patenaude to testify as an
expert. We are not persuaded that the district court abused its
discretion when it allowed the testimony. The court conducted
a lengthy voir dire examination of Dr. Patenaude, and Defen-
dants have failed to cite controlling authority that doctors with
Dr. Patenaude’s qualifications are categorically ineligible to
testify to their professional opinions.

  On appeal, REVERSED and REMANDED for a new trial.
On cross-appeal, AFFIRMED. Costs on appeal awarded to
Plaintiff.
