                                   In the

       United States Court of Appeals
                    For the Seventh Circuit
                        ____________________
No. 15-2393
MATTHEW SCHAEFER, et al.,
                                                   Plaintiffs-Appellants,
                                     v.

UNIVERSAL SCAFFOLDING & EQUIPMENT, LLC,
et al.,
                                    Defendants-Appellees.
                        ____________________

            Appeal from the United States District Court for the
                        Southern District of Illinois.
            No. 10-cv-791 — Philip M. Frazier, Magistrate Judge.
                        ____________________

   ARGUED JANUARY 14, 2016 — DECIDED OCTOBER 7, 2016
                ____________________

   Before FLAUM and RIPPLE, Circuit Judges, and PETERSON,
District Judge.∗
    PETERSON, District Judge. This diversity case requires us to
review the district court’s application of Illinois tort law, par-
ticularly concerning spoliation of evidence. Matthew
Schaefer, a construction worker, alleges that he was seriously

   ∗   Of the Western District of Wisconsin, sitting by designation.
2                                                 No. 15-2393

injured when a defective piece of scaffolding fell and struck
him on the head. So, in addition to bringing a workers’ com-
pensation claim against his employer, Schaefer sued the scaf-
folding manufacturer, Universal Scaffolding & Equipment,
LLC. When he learned that the piece of scaffolding that hit
him had been lost, he added claims for negligent spoliation
of evidence against his employer, Brand Energy Services,
LLC, and against Dynegy Midwest Generation, LLC, the
company that had engaged Brand to build scaffolding at a
Dynegy power plant. Schaefer also alleged claims for con-
struction negligence and failure to warn against Dynegy.
Schaefer’s wife joined his claims for negligent spoliation and
brought claims for loss of consortium against each of the de-
fendants.
    In a series of decisions, the district court granted sum-
mary judgment for defendants. At the heart of the case is the
missing piece of scaffolding, which had been lost while in
Dynegy’s possession, before anyone had tested it for defects.
The district court held that without the missing piece,
Schaefer could not prove his product liability claims against
Universal. The district court also held that Dynegy was not
liable for any defects or negligence in the construction of the
scaffolding. We affirm these decisions.
    But the district court also held that Schaefer and his wife
could not prove their spoliation claims either, reasoning that
because the Schaefers were unable to prove that the missing
piece was in fact defective, they would be unable to prove
that the loss of the piece caused them any damage. The dis-
trict court here relied on an incorrect statement of Illinois
spoliation law, which does not require a plaintiff to prove
that he would have won his case but for the spoliation. A
No. 15-2393                                                3

spoliation claim under Illinois law requires only that the
plaintiff show a “reasonable probability” of success on the
underlying suit. Because the Schaefers adduced evidence
from which a jury could make this finding—the batch of
scaffolding used on the Dynegy project had a large number
of defective pieces—the grant of summary judgment on the
spoliation claims was improper. Accordingly, we reverse the
grant of summary judgment on the spoliation claims against
Brand and Dynegy.
                       I. Background
   Matthew Schaefer was an employee of Brand Energy
Services, LLC, which had been engaged by Dynegy Midwest
Generation, LLC, to erect scaffolding at a Dynegy power
plant. Under its contract with Dynegy, Brand had complete
and authoritative control over the scaffold construction.
Ryan Wampler was Brand’s project manager. Dynegy also
had a safety manager at the power plant, Don Watson. Brand
acquired the scaffold components from Universal Scaffold-
ing & Equipment, LLC, but Dynegy paid for the scaffolding
and owned it.
     The Universal scaffolding used a “cup-lock” system in
which metal tabs on the horizontal bars, called “ears,” would
fit into a cup attached to the vertical members. A second cup
would be locked down onto the ears to hold the components
in place. Brand workers had difficulties with the Universal
scaffolding components because some of the bars were not
the proper length and some had bent ears, and those faulty
components would not readily lock into the cups. Eventually
the problem became prevalent enough that Wampler had his
crew inspect the new Universal components as they arrived
and then mark and set aside the defective pieces.
4                                                 No. 15-2393

    At the time of Schaefer’s accident, November 2008,
Schaefer and other Brand employees, including Maynard
Hudson, were assembling scaffolding. Schaefer was a level
below Hudson. A laborer would hand Schaefer a piece of
scaffolding, and Schaefer would hand it up to Hudson, who
would assemble the pieces. Hudson placed a three-foot, six-
inch horizontal bar in the cups; but when he placed the next
bar, the three-foot, six-inch bar popped out of its cups, fell,
and struck Schaefer on the head. Schaefer suffered serious
injuries to his neck, back, shoulders, and arms.
    Precisely what caused the bar to fall is sharply disputed.
Neither Schaefer nor Hudson noticed any defects in the bars,
although during the assembly process they did not have
time to look carefully. Wampler investigated the accident,
and he reported that Hudson had knocked the bar with his
hip or tool bag; but Hudson denies this. Schaefer contends
that the root cause was Universal’s defective scaffolding, but
proving that theory is problematic because of what hap-
pened to the bar.
    Immediately after Schaefer’s accident, Watson (Dynegy’s
safety manager) asked Wampler to retrieve the bar that
struck Schaefer. Watson stored the bar in his office at the
power plant. When he moved offices in December 2009, he
left the bar behind, and it was eventually moved to a storage
room in the power plant. The last time that anyone saw the
bar was in September or October of 2010, when a safety
worker saw it in the storage room. By November 2011, the
first time that Schaefer sought to examine the bar as part of
discovery in this case, it had been lost.
   Schaefer filed a workers’ compensation claim in March
2009. He filed a discovery action against Brand in Illinois
No. 15-2393                                                    5

state court in December 2009. Brand never responded to the
suit or to Schaefer’s interrogatories asking who had sold
Brand the scaffolding used at the construction site and what
the company had done with the scaffolding after finishing
the project. Schaefer did not press the discovery action.
    In June 2010, Schaefer and his wife, Cynthia, filed a com-
plaint against Universal in state court, bringing claims for
negligence, strict liability for product defect, strict liability
for failure to warn, and loss of consortium. (Both Matthew
and Cynthia Schaefer are plaintiffs and appellants, but for
simplicity, we will refer to them collectively as “the
Schaefers,” and we will refer to Matthew as “Schaefer.”)
Universal removed the case to federal court on the basis of
diversity. Two amended complaints later, Schaefer had six
causes of action under Illinois law: three against Universal
for negligence (product liability), strict liability for product
defect, and strict liability for failure to warn; two against
Dynegy for negligence and negligent spoliation; and one
against Brand for negligent spoliation. Schaefer’s wife also
brought three claims of her own: one against Dynegy for
negligent spoliation; one against Brand for negligent spolia-
tion; and one against all defendants for loss of consortium.
   The district court granted summary judgment to defend-
ants on all claims in a series of decisions issued over the
course of two years. In June 2013, a now-retired district
judge denied Brand’s motion for summary judgment on the
spoliation claim against it. In February 2014, the district
judge who took over the case denied cross-motions from the
Schaefers and from Brand and Dynegy for summary judg-
ment on the spoliation claims, but he granted Universal’s
motion for summary judgment on all claims against it.
6                                                  No. 15-2393

    The parties then consented to have a magistrate judge
preside over the remainder of the case (i.e., the claims
against Dynegy and Brand). In January 2015, the magistrate
judge granted Dynegy’s motion for summary judgment on
Schaefer’s negligence claim against it. A month later, as the
case neared trial on the remaining claims for spoliation and
loss of consortium, the magistrate judge granted Brand and
Dynegy’s joint motion in limine to exclude all evidence and
testimony that the missing scaffolding bar was defective. At
the magistrate judge’s invitation, Brand and Dynegy re-
newed their motions for summary judgment on the spolia-
tion and loss of consortium claims. The magistrate judge
granted Brand and Dynegy’s renewed motion and the case
was over. This appeal followed.
                        II. Discussion
    The Schaefers contend that the district court erred in en-
tering summary judgment on each of their claims. We re-
view the district court’s grant of summary judgment de no-
vo, examining the record in the light most favorable to the
Schaefers. Carson v. ALL Erection & Crane Rental Corp., 811
F.3d 993, 995 (7th Cir. 2016). Under Federal Rule of Civil Pro-
cedure 56, summary judgment is appropriate only when
there are no genuine disputes of material fact and the mov-
ing party is entitled to judgment as a matter of law.
    A. Product liability and negligence claims
    We begin with Schaefer’s product liability claims against
Universal. Relying on Shramek v. General Motors Corp., Chev-
rolet Motor Division, 69 Ill. App. 2d 72, 216 N.E.2d 244 (1966),
and its progeny, the district court concluded that product
liability claims fail under Illinois law when the plaintiff does
No. 15-2393                                                    7

not present the allegedly defective product itself, or at least
other admissible evidence that the product was defective.
On appeal, Schaefer contends that the district court erred in
concluding that he lacked evidence that the bar was defec-
tive. We disagree.
    Under Illinois law, plaintiffs in product liability actions
“must identify the manufacturer of the product and demon-
strate a causal relationship between the injury and the man-
ufacturer’s product.” Tragarz v. Keene Corp., 980 F.2d 411, 418
(7th Cir. 1992) (citing Zimmer v. Celotex Corp., 192 Ill. App. 3d
1088, 1091, 549 N.E.2d 881, 883 (1989)). As part of proving a
causal relationship, Schaefer must adduce evidence that the
bar was, in fact, defective. This evidence can be direct or cir-
cumstantial, but Schaefer must establish that a defect in the
scaffolding caused the accident. Shramek, 216 N.E.2d at 247;
see also Sanchez v. Firestone Tire & Rubber Co., 237 Ill. App. 3d
872, 874, 604 N.E.2d 948, 950 (1992) (“Proper circumstantial
evidence includes either proof that tends to exclude other
extrinsic causes or expert testimony that the product was de-
fective.”). The mere fact that an accident occurred does not
establish causation. Shramek, 216 N.E.2d at 247.
    Schaefer relies on deposition testimony from four wit-
nesses, arguing that this testimony creates a genuine dispute
of material fact as to whether the bar was defective. But
these witnesses merely confirm that workers at the construc-
tion site had identified some defective scaffolding pieces.
The record does not establish that every piece of scaffolding
at the jobsite was defective, and there is no evidence in the
record that the specific bar that caused Schaefer’s injury was
defective. And one of Schaefer’s own experts, Geno Mani-
ago, conceded at his deposition that even if that specific bar
8                                                             No. 15-2393

had been defective, the bar could have been damaged at the
work site, which would mean that the defect was not at-
tributable to Universal.
    Without the bar itself, which was lost before it was ana-
lyzed, Schaefer cannot prove that Universal’s defective
product caused his injuries, and thus he cannot succeed on
his product liability claims against Universal. At most, he
has adduced expert opinions that the bar that hit him might
have been one of the defective ones. But this is not enough to
get the case to a jury. See Sanchez, 604 N.E.2d at 950
(“[L]iability in a products liability action cannot be based on
mere speculation, guess, or conjecture, and the circumstanc-
es shown must justify an inference of probability as distin-
guished from mere possibility.”); Phillips v. U.S. Waco Corp.,
163 Ill. App. 3d 410, 419, 516 N.E.2d 670, 675 (1987) (“With-
out an examination of the scaffold itself to determine if the
collapse was a result of a preexisting defect, Phillips could
never prove, directly or inferentially, a claim based in negli-
gence or strict liability.”). The district court properly granted
summary judgment to Universal on Schaefer’s product lia-
bility claims. And, consequently, Cynthia Schaefer’s loss of
consortium claim against Universal necessarily fails, and the
district court properly granted summary judgment on that
claim, too. 1



    1  Under Illinois law, “actions for personal injuries and actions for
loss of consortium … are legally distinct.” Mitchell v. White Motor Co., 58
Ill. 2d 159, 163, 317 N.E.2d 505, 507 (1974). But when a defendant is not
liable for the underlying claim, it is appropriate to dismiss attached
claims for loss of consortium. See, e.g., Fluker v. County of Kankakee, 945 F.
Supp. 2d 972, 994 (C.D. Ill.), aff’d, 741 F.3d 787 (7th Cir. 2013).
No. 15-2393                                                  9

    This leaves Schaefer’s negligence claim against Dynegy.
As a general rule of Illinois law, a party who hires an inde-
pendent contractor is not liable for the acts of the independ-
ent contractor. Wilfong v. L.J. Dodd Const., 401 Ill. App. 3d
1044, 1060, 930 N.E.2d 511, 526 (2010). Dynegy hired Brand
to build the scaffolding, so if the general rule applies,
Dynegy is not liable for the defective construction. On ap-
peal, Schaefer gives three reasons (the same reasons he gave
to the district court) why the general rule should not apply.
We are not persuaded.
   Schaefer relies first on the “retained control” exception to
the general rule, as articulated in § 414 of the Restatement
(Second) of Torts, which Illinois has adopted. Section 414
provides:
      One who entrusts work to an independent con-
      tractor, but who retains the control of any part
      of the work, is subject to liability for physical
      harm to others for whose safety the employer
      owes a duty to exercise reasonable care, which
      is caused by his failure to exercise his control
      with reasonable care.
Restatement (Second) of Torts § 414 (1965). Schaefer con-
tends that Dynegy retained enough control over Brand’s
work that Dynegy owed him a duty to exercise reasonable
care over the scaffolding project.
    Schaefer argues that Dynegy exercised control through
Watson, Dynegy’s on-site safety director at the power plant.
According to Schaefer, Watson “would walk around the job
site, talk to workers and try to correct unsafe things.” Appel-
lants’ Brief, at 35. Watson’s authority, according to Schaefer,
10                                                                  No. 15-2393

was conferred through the Master Services Agreement
(MSA), under which “Dynegy reserve[d] the right to inspect
and deny access or use of any equipment or substance
brought on site.” Id. at 9 (citing Dkt. 197-6). 2 The MSA also
required Brand to participate in Dynegy’s safety program.
    But Watson’s work and Dynegy’s safety program estab-
lish only that Dynegy had a right to inspect and to require
general safety. The comments to § 414 make clear that retain-
ing these general rights do not give rise to liability under the
retained control exception. As comment C provides:
           In order for the rule stated in this Section to
           apply, the employer must have retained at
           least some degree of control over the manner
           in which the work is done. It is not enough that
           he has merely a general right to order the work
           stopped or resumed, to inspect its progress or
           to receive reports, to make suggestions or rec-
           ommendations which need not necessarily be
           followed, or to prescribe alterations and devia-
           tions. Such a general right is usually reserved
           to employers, but it does not mean that the
           contractor is controlled as to his methods of
           work, or as to operative detail. There must be
           such a retention of a right of supervision that
           the contractor is not entirely free to do the
           work in his own way.
Restatement (Second) of Torts § 414, Comment C.




     2   All docket citations refer to the district court docket.
No. 15-2393                                                    11

    Schaefer contends that Watson’s activities are compara-
ble to those that were sufficient to show “retained control”
in Bokodi v. Foster Wheeler Robbins, Inc., 312 Ill. App. 3d 1051,
728 N.E.2d 726 (2000). But in Bokodi, “defendants’ actions in-
dicated a substantial level of involvement in the incidental
activities at the work site.” 728 N.E.2d at 735. Watson’s safe-
ty inspection activities, which extended to the entire plant
and not just to the scaffolding project, did not get him in-
volved in incidental activities of the scaffold construction.
The contract between Dynegy and Brand expressly gave
Brand control:
       Contractor is, and shall continue to be, an in-
       dependent contractor, and any provisions of
       this Agreement or any Purchase Order which
       may appear to give Dynegy the right to direct
       Contractor as to details of performing any Ser-
       vices, or to exercise a measure of control over
       Contractor’s performance of the Services, shall
       be interpreted to mean that Contractor will fol-
       low the instructions of Dynegy with respect to
       the results of the Services achieved only and
       not in the means whereby the Services are to be
       accomplished. Contractor shall have complete and
       authoritative control as to the details of performing
       the Services.
Dkt. 197-6, at 12 (MSA, § A.23) (emphasis added). Other sec-
tions of the contract gave Dynegy the right to inspect
Brand’s work and to halt work when unsafe, but the contract
did not give Dynegy control over operational details of the
scaffold construction. Without control over operational de-
tails, the right of inspection and the authority to stop work is
12                                                   No. 15-2393

insufficient to establish “retained control” under § 414 of the
Restatement. Moiseyev v. Rot's Bldg. & Dev. Inc., 369 Ill. App.
3d 338, 351, 860 N.E.2d 1128, 1139 (2006). And when, as in
this case, the evidence establishes only the right to inspect, to
halt work, and to make safety suggestions, the question is
decidable as a matter of law. Id. at 1139‒40.
    Second, Schaefer contends that Dynegy, as the landown-
er, is liable for unsafe conditions on its premises. But
Schaefer devotes only a scant paragraph to the issue. He
cites no authority and simply asserts that the ill-fitting scaf-
folding components constitute a condition of the land. Per-
functory and undeveloped arguments are waived, as are ar-
guments unsupported by legal authority. United States v.
Hook, 471 F.3d 766, 775 (7th Cir. 2006).
     But Schaefer’s argument would fail even if not waived.
Illinois courts have adopted §§ 343 and 343A of the Restate-
ment (Second) of Torts for purposes of evaluating premises
liability claims. Cooper v. Carl A. Nelson & Co., 211 F.3d 1008,
1015 (7th Cir. 2000), as amended on denial of reh’g and reh’g en
banc, (June 1, 2000) (citing Genaust v. Ill. Power Co., 62 Ill. 2d
456, 468, 343 N.E.2d 465, 472 (1976)). These provisions im-
pose liability on landowners, under certain circumstances,
for harm caused “by a condition on the land.” Restatement
(Second) of Torts § 343. But not everything located on a
landowner’s property is a “condition on the land.” See, e.g.,
Gregory v. Beazer E., 384 Ill. App. 3d 178, 191, 892 N.E.2d 563,
577 (2008) (asbestos blankets and gloves were not conditions
on the land); Quinton v. Kuffer, 221 Ill. App. 3d 466, 472, 582
N.E.2d 296, 300 (1991) (a flammable 55-gallon drum that ex-
ploded was not a condition on the land). Schaefer was not
injured by already-assembled scaffolding, which could ar-
No. 15-2393                                                  13

guably be a condition on the land. He alleges that he was in-
jured as a result of an activity taking place on the Dynegy
property, one that involved a defective piece of equipment.
The cause of Schaefer’s injury is unlike those things that con-
stitute conditions on the land, so premises liability is a poor
fit for Schaefer’s negligence claim against Dynegy.
    Schaefer’s third basis for holding Dynegy liable is a “fail-
ure to warn” theory. The Illinois Supreme Court has applied
§ 388 of the Restatement (Second) of Torts to failure to warn
claims. See Busch v. Graphic Color Corp., 169 Ill. 2d 325, 348,
662 N.E.2d 397, 409 (1996). Under § 388, in certain circum-
stances, one who provides chattel for another to use has a
duty to warn of known defects in the chattel. Schaefer con-
tends that Dynegy should have warned him about the defec-
tive scaffolding. The district court held that Schaefer could
not proceed under this theory of negligence because he had
failed to adduce evidence of any unequal knowledge be-
tween Schaefer and Dynegy. The district court was correct.
   Under Illinois law, “[a] duty to warn exists where there is
unequal knowledge, actual or constructive of a dangerous
condition, and the defendant, possessed of such knowledge,
knows or should know that harm might or could occur if no
warning is given.” Happel v. Wal-Mart Stores, Inc., 199 Ill. 2d
179, 186, 766 N.E.2d 1118, 1123 (2002) (citations, internal
quotation marks, and alterations omitted). Schaefer’s
knowledge of the defective scaffolding was undisputedly
equal to, and likely much greater than, Dynegy’s knowledge.
By the time of the accident, Brand workers had already had
several problems with the scaffolding. Brand’s project su-
pervisor Wampler (Schaefer’s boss) had directed Brand
workers to go through new shipments of scaffolding, mark
14                                                        No. 15-2393

the bad pieces, and set them aside. Wampler had also talked
to his crews about the bad scaffolding. Schaefer himself testi-
fied that he had noticed problems with the scaffolding on the
jobsite. As for the specific bar that struck him, Schaefer han-
dled it when he passed it up to Hudson to put it into place.
Because Schaefer had at least as much knowledge as Dynegy
had about the bar’s defects, Schaefer’s failure to warn theory
necessarily fails. 3 And with that, Schaefer’s negligence claim
against Dynegy is doomed, along with his wife’s related loss
of consortium claim.
    In sum, based on undisputed facts of the record, the dis-
trict court properly granted summary judgment on
Schaefer’s product liability claims against Universal and his
negligence claim against Dynegy.
     B. Spoliation claims
    The Illinois Supreme Court recognized a cause of action
for negligent spoliation of evidence in Boyd v. Travelers Insur-
ance Co., 166 Ill. 2d 188, 193, 652 N.E.2d 267, 270 (1995), as
modified on denial of reh’g, (June 22, 1995). In that case, the
plaintiff, Boyd, was injured in an explosion that he alleged
was caused by a defective propane heater. Insurance com-
pany employees took the heater for testing to determine the
cause of the explosion, but the heater was lost while in the
insurance company’s possession, before it had been tested
for defects. Boyd brought spoliation claims against the in-


     3It bears mentioning that Schaefer’s arguments in support of his
negligence claim against Dynegy generally presume that the bar was
defective. But without the bar, he cannot prove that it was defective, so
his negligence claim against Dynegy would fail for the same reason that
his product liability claims against Universal fail.
No. 15-2393                                                 15

surance company, which the insurance company moved to
dismiss. The case was certified to the Illinois Supreme Court,
which held for the first time that Illinois recognizes a claim
for negligent spoliation, and that Boyd had stated such a
claim, even though he would not be able to prove that the
heater was actually defective. Boyd, 652 N.E.2d at 272.
    Under Boyd, spoliation is not a separate, new tort, but a
species of negligence. Accordingly, a negligent spoliation
claim requires the plaintiff to prove the traditional four ele-
ments of negligence: a duty to preserve the evidence; breach
of that duty by loss of the evidence; that the loss proximately
caused the plaintiff’s inability to prove his underlying claim;
and actual damages as a result. Id. at 270; see also Martin v.
Keeley & Sons, Inc., 2012 IL 113270, ¶ 26, 979 N.E.2d 22, 27.
    In this case, the district court twice denied motions for
summary judgment on the Schaefers’ spoliation claims. A-8‒
16. The district court held that both Brand and Dynegy had a
duty to preserve the scaffolding piece, but that questions of
fact about the other elements precluded summary judgment
for either side. As trial approached, Brand and Dynegy filed
a joint motion in limine to exclude any evidence or argument
that the scaffolding was defective. Dkt. 220. The motion
prompted the district court (now with Magistrate Judge Fra-
zier presiding) to revisit the proximate cause issue. The dis-
trict court granted the motion in limine, reasoning that with-
out the missing scaffolding piece, the Schaefers could never
prove by a preponderance of the evidence that the loss of the
bar caused them to lose their underlying claims. With that
evidentiary ruling made, the Schaefers’ spoliation claims
were doomed. The court invited Brand and Dynegy to re-
16                                                   No. 15-2393

new their motions for summary judgment and granted
them.
    On appeal, the Schaefers contend that the district court
applied the wrong legal standard to their spoliation claims,
which led the court to incorrectly grant the motion in limine.
The Schaefers contend that they had adduced admissible ev-
idence that the bar was defective, and thus they should have
been allowed to proceed to trial on their negligent spoliation
claims. Brand and Dynegy disagree, and they contend that
the district court also erred in its earlier decisions that they
had a duty to preserve the bar. We may affirm a district
court’s grant of summary judgment based on any ground
that the record supports, so long as the non-moving party
had the opportunity to contest the issue. Gerhartz v. Richert,
779 F.3d 682, 685 (7th Cir.), cert. denied, 136 S. Ct. 319 (2015).
Accordingly, we consider both issues, duty and causation.
     1. Duty
   Illinois law imposes no general duty to preserve evi-
dence, but a duty arises if two conditions are satisfied. First,
a “relationship” condition: the duty must “arise[] by agree-
ment, contract, statute, special circumstance, or voluntary
undertaking.” Dardeen v. Kuehling, 213 Ill. 2d 329, 336, 821
N.E.2d 227, 231 (2004). Second, a “foreseeability” condition:
the duty to preserve must “extend[] to the evidence at is-
sue—i.e., whether a reasonable person should have foreseen
that the evidence was material to a potential civil action.” Id.
A plaintiff must satisfy both the relationship condition and
the foreseeability condition to prove that a duty to preserve
evidence existed. Id.
No. 15-2393                                                  17

    The foreseeability condition is straightforward here: both
Brand and Dynegy knew that the bar was involved in a seri-
ous workplace injury, which is why Dynegy’s Watson
sought to preserve it in the first place. Dynegy contends that
the foreseeability condition had “expired,” so to speak, by
the time Dynegy lost the bar in October 2010, because
Schaefer had not asked Dynegy for the bar by then, and no
one in Dynegy’s position would think that the bar mattered
anymore. But that is merely conclusory. We agree with the
district court that Dynegy, having collected the bar because
of its role in a workplace accident, could not simply assume
after less than two years that the bar was no longer pertinent
to a personal injury claim.
    The relationship condition is more complex. As one dis-
trict court in this circuit has recently observed, “Illinois
courts have not precisely defined what constitutes a ‘special
circumstance,’ but ‘something more than possession and
control are required, such as a request by the plaintiff to pre-
serve the evidence and/or the defendant’s segregation of the
evidence for the plaintiff[’]s benefit.’” Hart v. Amazon.com,
Inc., No. 15-cv-1217, 2015 WL 8489973, at *6 (N.D. Ill. Dec. 8,
2015) (quoting Martin, 979 N.E.2d at 31). It would be an un-
derstatement to say that this area of Illinois law is not gov-
erned by bright-line rules. But Martin makes clear that mere
possession of the evidence is not enough to impose a duty.
979 N.E.2d at 31‒32. Nor is being the plaintiff’s employer, or
being a potential litigant. Id. But a request by a plaintiff to
preserve the evidence, or a defendant’s segregation of the
evidence for the plaintiff, are recognized as special circum-
stances. Id.
18                                                 No. 15-2393

    For Brand, those special circumstances are present, alt-
hough in a factually complicated way. Brand did not take
long-term possession of the bar. But after the accident,
Wampler, Brand’s project supervisor, collected the bar and
delivered it to Watson, Dynegy’s safety supervisor, for safe-
keeping because of its role in Schaefer’s accident. Schaefer
filed a discovery action against Brand in December 2009. His
discovery requests did not ask Brand to produce the bar it-
self, but Schaefer was plainly seeking information about the
bar, which at the time Brand knew was in Dynegy’s posses-
sion. Brand contends now that Schaefer’s discovery com-
plaint was legally unsound, and that Brand was entitled to
ignore it. Maybe so, but the potential infirmities of the dis-
covery action are beside the point. What matters is that a lit-
tle more than a year after Schaefer’s accident, Brand knew
that Schaefer was looking to Brand for information about the
allegedly defective bar, which Brand had collected and de-
livered to Dynegy to preserve. These facts bring the case
close to Miller v. Gupta, 174 Ill. 2d 120, 129, 672 N.E.2d 1229,
1233 (1996), where analogous special circumstances satisfied
the relationship prong. In Miller, the plaintiff’s attorney re-
quested X-rays from the plaintiff’s doctor, and the doctor
collected them. But the cleaning staff inadvertently tossed
them out before copies were provided to plaintiff’s attorney.
The district court here was right: having collected the bar,
and knowing that Schaefer was looking for it, Brand had a
duty to preserve it.
    We reach the same conclusion with regard to Dynegy be-
cause Dynegy voluntarily assumed a duty to preserve the
bar. “A voluntary undertaking requires a showing of affirm-
ative conduct by the defendant evincing defendant’s intent
to voluntarily assume a duty to preserve evidence.” Martin,
No. 15-2393                                                 19

979 N.E.2d at 28. Dynegy knew that Schaefer had been in-
jured when the bar fell on him, and Watson asked a Brand
employee to retrieve the bar so that Watson could store it in
his office so that “there wasn’t any issue later.” And Watson
recognized the potential importance of the bar to Schaefer’s
case: sometime after the accident, Watson went to the inter-
net to find out how much the bar weighed and what amount
of force it had when it fell and struck Schaefer. Dynegy took
affirmative steps to take possession of the bar, and to save it
for potential litigation. Thus, Dynegy’s voluntary undertak-
ing satisfies the relationship condition of the duty analysis.
   2. Causation
    We turn now to whether the district court applied the
correct standard for causation, and whether under the cor-
rect standard, the Schaefers had raised a genuine issue of
fact regarding whether the loss of the bar was the proximate
cause of Schaefer’s inability to prove his underlying negli-
gence claims.
   Causation in a spoliation case is a subtle concept. Under
the principles set out in Boyd, the spoliation plaintiff has to
prove that the loss of the evidence would cause him to lose
the underlying case. 652 N.E.2d at 271. This showing pre-
vents a spoliation claim from succeeding on the loss of some
inconsequential evidence. But, as explained in a critical foot-
note in Boyd, the spoliation plaintiff does not have to prove
that he would have actually won his case with the missing
piece:
      A plaintiff need not show that, but for the loss
      or destruction of the evidence, the plaintiff
      would have prevailed in the underlying action.
20                                                  No. 15-2393

       This is too difficult a burden, as it may be im-
       possible to know what the missing evidence
       would have shown.
Id. at 271 n.2. If the spoliation plaintiff had to prove that he
would have won the underlying suit if he had the missing
evidence, he would be in a hopeless Catch-22: if he could
prove that he would have won the underlying case even
without the lost evidence, then he could not show that the
loss of that evidence actually harmed him. In other words, it
would be impossible for the spoliation plaintiff to show both
that without the lost evidence he would necessarily lose the
underlying case, and that with it, he would win.
    So, to prevail on their spoliation claims, the Schaefers
must make two showings. First, they must show that the loss
of the scaffolding piece would cause them to lose their un-
derlying suit. Id. And second, they must show that if they
had the scaffolding piece, they would have a “reasonable
probability” of winning. Id. But “reasonable probability” is
less than proof of success by a preponderance of the evi-
dence, because that is the standard required to show that
they would have won the underlying suit.
    Boyd makes clear that the burden is on the Schaefers to
make these showings; there is no evidentiary presumption
that negligently lost evidence is favorable to the plaintiff. Id.
at 273. Although the burden is on the plaintiff, if a defendant
shows that the plaintiff could not win the underlying suit
even with the lost evidence, then the spoliation claim neces-
sarily fails. Id. at 271 n.2. Causation in a negligence case is
generally question for the trier of fact, unless there is no ma-
terial dispute or only one conclusion is clearly evident. Wil-
No. 15-2393                                                    21

liams v. Univ. of Chi. Hosps., 179 Ill. 2d 80, 88, 688 N.E.2d 130,
134 (1997).
    The magistrate judge in this case held the Schaefers to the
wrong standard. The magistrate judge correctly acknowl-
edged that to succeed on the spoliation claims, Boyd “would
require plaintiff to show a reasonable probability of success”
on the underlying negligence claims. A-42. But the magis-
trate judge conflated reasonable probability of success with
proof by a preponderance of the evidence:
       And plaintiff must prove a reasonable proba-
       bility of success on the merits. Now I have a
       hard time distinguishing in my mind any qual-
       itative difference between reasonable probabil-
       ity of success on the merits and the ability to
       show a preponderance of the evidence. Both
       mean more likely than not.
A-40. The magistrate judge also incorrectly paraphrased the
holding in Boyd: “Or I think another way that it was put in
Boyd is that, but for the loss of the scaffolding they would
have been able to succeed on their claims.” A-42. This con-
tradicts the actual holding in Boyd, which is that a spoliation
plaintiff need not prove that he would have succeeded on
the underlying claim but for the loss of the evidence.
   Applying the proper standard, and viewing the record in
the light most favorable to the Schaefers (as we must on the
defense motions for summary judgment), the Schaefers have
adduced sufficient evidence to put the issue of causation into
genuine dispute. There was a pervasive problem with the
scaffolding at the Dynegy jobsite, and workers were having
ongoing problems with the horizontal bars popping out of
22                                                No. 15-2393

cups. The problem got so bad that Brand’s project supervisor
had workers go through each new shipment of scaffolding
and set aside the bad pieces. No one has provided testimony
that the bar that hit Schaefer was actually defective. Several
employees testified that they did not notice any defects in
the bar that fell on Schaefer, but there is ample testimony
that the defects would not be readily apparent after only a
quick glance, which is all that Schaefer and his colleagues
had time for while assembling the scaffolding. Hudson, the
employee who installed the bars involved in the accident,
testified that he did not bump any of them, despite
Wampler’s report. If the jury were to believe Hudson, a rea-
sonable jury could eliminate his negligence as a cause of the
accident. It may be impossible for Schaefer to prove his neg-
ligence case without the missing evidence, but the finger of
suspicion points distinctly toward the missing bar, just as it
pointed to the missing propane heater in Boyd. If Schaefer’s
experts had had the opportunity to test the missing piece,
they might have been able to confirm that the piece had de-
fects that had gone unnoticed by the lay witnesses at the
jobsite. But the loss of the piece deprived Schaefer of the op-
portunity to develop this important proof.
   We conclude that the Schaefers have raised a genuine is-
sue of fact as to whether, with the missing scaffolding, they
would have had a reasonable probability of success on their
underlying claims. The district court’s grant of summary
judgment on this issue is reversed.
     3. Motion in limine
   Our ruling necessarily means that the district court also
erred in granting the joint motion in limine No. 21, which
excluded all evidence that the missing piece was defective.
No. 15-2393                                                    23

We review rulings on motions in limine for abuse of discre-
tion; decisions about admitting and excluding evidence “are
peculiarly within the competence of the district court.” Von
der Ruhr v. Immtech Int’l, Inc., 570 F.3d 858, 862 (7th Cir. 2009)
(citations and internal quotation marks omitted). But we will
overturn the district court’s ruling if it is based on the wrong
legal standard. See Aldridge v. Forest River, Inc., 635 F.3d 870,
875 (7th Cir. 2011) (“[T]he district court’s decision [on a mo-
tion in limine] is to be overturned only if no reasonable per-
son would agree with the trial court’s ruling.”).
    The district court’s ruling on motion in limine No. 21 was
based on the notion that any evidence that the missing scaf-
folding was defective would be necessarily speculative. The
district court’s reason for excluding Schaefer’s experts was
that they could not reliably testify that the missing scaffold-
ing actually had any of the defects that had been common in
the Universal scaffolding at the work site:
       I’m not going to allow Maniago or Unger to of-
       fer any opinion as to any defect that existed or
       that the defect may have caused the accident to
       happen, the incident to happen for the simple
       reason that, by their own admission and just by
       the application of just common sense, is that,
       that is just purely speculation on their part.
A-45. Both Maniago and Unger conceded that without the
opportunity to test the lost scaffolding piece they could not
say whether it was defective. But that is part of the showing
that the Schaefers had to make to support their spoliation
claims. They offered Maniago and Unger to help explain
how the scaffolding worked, and to offer explanations of
how the alleged defects in the scaffolding could have caused
24                                                No. 15-2393

the bar to fall and thereby cause Schaefer’s injuries. Mani-
ago’s and Unger’s testimony could have been admitted for
these purposes, even if they could not testify whether the
missing bar was actually defective. And the prevalence of
defects among the Universal scaffolding pieces at the
worksite certainly makes it more likely that the piece that hit
Schaefer was defective. The district court’s grant of motion
in limine No. 21, excluding all evidence that the missing
scaffolding was defective, was in error because it evaluated
the relevance of their testimony under the wrong legal
standard applicable to spoliation claims.
     This is not to say that Maniago’s and Unger’s testimony
must be admitted. On remand, the parties may revisit their
qualifications and the reliability of their testimony. But the
district court must evaluate these issues under the correct
standard for evaluating a negligent spoliation claim under
Illinois law.
                       III. Conclusion
    For the foregoing reasons, we AFFIRM the entry of
summary judgment on all claims against Universal, and the
entry of summary judgment on Schaefer’s negligence claim
and Cynthia Schaefer’s related loss of consortium claim
against Dynegy. We REVERSE the grant of summary judg-
ment on the Schaefers’ spoliation claims against Dynegy and
Brand. We REMAND for further proceedings consistent with
this opinion.
