Introduction

In James B. Riley v. Tesla, Inc. (Court of Appeals for the Eleventh Circuit, Mar. 21, 2025) the Eleventh Circuit affirmed a series of district court rulings that together deliver two practical and important clarifications for Florida product liability litigation and federal expert practice:

• Florida’s “but-for” causation standard applies to design-defect claims predicated on fire-spread mitigation (here, the absence of fire-retardant intumescent material in an EV battery pack). The “substantial factor” formulation is reserved for rare, truly independent concurring causes.
• Federal courts will strictly police expert disclosures and reliability under Rules 26, 37, and 702: untimely “supplemental” affidavits that materially alter methodology or certainty are subject to exclusion, and expert opinions must rest on sufficient facts/data, reliable methods, and accident-specific application.

The case stems from a tragic 2018 crash in which 18-year-old Barrett Riley, driving a 2014 Tesla Model S P85D at 116 mph into a curve, lost control and collided multiple times before a fire erupted. Barrett died from thermal injuries. The estate, through James Riley, sued Tesla under negligence (removal of a parent-requested speed limiter) and under product liability theories alleging: (1) the cylindrical lithium-ion cell walls were too thin to prevent fire on impact; and (2) the battery pack lacked intumescent material to prevent fire spread.

The district court struck the estate’s expert’s late supplemental affidavit, excluded the expert’s “cell wall thickness” defect opinion under Federal Rule of Evidence 702, and ultimately granted summary judgment to Tesla on both sets of product claims—first for lack of admissible defect evidence (cell wall theory), and later for lack of causation evidence (intumescent theory). A jury later awarded damages on the remaining negligence claim, but assigned only 1% fault to Tesla. The Eleventh Circuit affirmed across the board.

Summary of the Opinion

• Supplemental affidavit struck (Rule 26/37): The expert’s “supplemental” affidavit—filed after the expert discovery deadline—introduced new methodological and certainty assertions (e.g., invoking “differential diagnosis” and stating opinions to a “reasonable degree of engineering certainty”). The court held it was untimely and improperly used to bolster a defective report, aligning with Guevara v. NCL (Bahamas) Ltd.
• Cell-wall thickness opinion excluded (Rule 702): The expert analyzed the wrong battery model, failed to measure the actual cell walls, could not justify a thickness standard, did not consider accident dynamics, and the only measurement in the record exceeded his own threshold. The opinion was not helpful, lacked sufficient facts/data, and did not apply reliable methods to the facts.
• Summary judgment on cell-wall defect claims: With the opinion excluded, there was no evidence of a defect/unreasonably dangerous condition under Florida law, warranting summary judgment.
• Summary judgment on intumescent-material claims: Even assuming reliability of the expert’s opinion that intumescent material would have slowed fire spread, the estate offered no evidence that Barrett would have survived “but for” its absence. Florida’s “substantial factor” test did not apply because the alleged defect was a dependent, not concurring, cause.
• Trial and judgment on negligence: The speed-limiter negligence claim proceeded to trial; the jury awarded $10.5 million but apportioned 90% fault to Barrett, 9% to James, and 1% to Tesla, resulting in a $105,000 net judgment for James under Florida’s comparative fault statute (Fla. Stat. § 768.81(3)).

Analysis

Precedents Cited and How They Shaped the Decision

• Expert disclosure and supplementation:
  • Guevara v. NCL (Bahamas) Ltd., 920 F.3d 710 (11th Cir. 2019): A party may not use a late “supplemental” affidavit to cure or bolster deficiencies after the deadline; district courts have broad discretion to exclude untimely expert material. The court applied Guevara to strike Dr. White’s late-filed affidavit, which introduced new methodological assertions and certainty levels responsive to Tesla’s criticisms.
  • Fed. R. Civ. P. 26(a)(2)(B), (D) and 26(e), 37(c)(1): Reports must contain a complete statement of opinions, bases, and data by court-ordered deadlines; untimely undisclosed material is excluded unless the failure is substantially justified or harmless. The estate showed neither.
  • Aldana v. Del Monte Fresh Produce N.A., Inc., 578 F.3d 1283 (11th Cir. 2009) and United States v. Shamsid-Deen, 61 F.4th 935 (11th Cir. 2023): The abuse-of-discretion standard permits a “range of permissible choices,” underscoring why contrasting district court outcomes elsewhere do not compel a different result here.
• Expert reliability (Rule 702/Daubert):
  • Fed. R. Evid. 702 and Daubert: The proponent must show the testimony will help the trier of fact, is based on sufficient facts or data, uses reliable principles and methods, and those principles are reliably applied to the case facts.
  • Kilpatrick v. Breg, Inc., 613 F.3d 1329 (11th Cir. 2010); Hughes v. Kia Motors Corp., 766 F.3d 1317 (11th Cir. 2014): Affirming exclusion where experts fail to ground causation opinions in reliable methods or neglect the accident’s multi-impact dynamics. Those authorities supported exclusion of Dr. White’s cell-wall opinion.
• Florida product liability: defect and causation:
  • R.J. Reynolds Tobacco Co. v. Nelson, 353 So. 3d 87 (Fla. Dist. Ct. App. 2022): A defect/unreasonably dangerous condition is required for both strict liability and negligent design; with the defect opinion excluded, the claim failed.
  • Gooding v. Univ. Hosp. Bldg., Inc., 445 So. 2d 1015 (Fla. 1984): The plaintiff must show it is “more likely than not” that the injury would not have occurred “but for” the defendant’s conduct; Florida does not permit recovery on a mere loss-of-chance theory.
  • Stahl v. Metro. Dade County, 438 So. 2d 14 (Fla. Dist. Ct. App. 1983): The substantial-factor test is a narrow exception for truly independent concurring causes that are each sufficient to cause the injury. Where causes are dependent, but-for causation governs.
  • Tieder v. Little, 502 So. 2d 923 (Fla. Dist. Ct. App. 1987); Starling v. City of Gainesville, 106 So. 425 (Fla. 1925): Multiple dependent causes warrant a but-for analysis.
  • Concurring-cause examples—Salazar v. Santos (Harry) & Co., 537 So. 2d 1048 (Fla. Dist. Ct. App. 1989) (two impacts either of which would be fatal); Sanders v. Am. Body Armor & Equip., 652 So. 2d 883 (Fla. Dist. Ct. App. 1995) (independently lethal gunshot wounds)—illustrate when substantial factor properly applies. The court explained why the intumescent-material theory did not fit that mold.

Legal Reasoning

The Eleventh Circuit’s analysis proceeded in three principal steps.

1. Striking the supplemental affidavit (Rules 26 and 37):

   Dr. White’s “supplement” was filed a month after the close of expert discovery and introduced new opinions in direct response to Tesla’s Daubert criticisms—specifically that he relied on a differential diagnosis and that his opinions were held to a reasonable degree of engineering certainty. Under Guevara and Rules 26(e)/37(c), courts may (and often should) exclude untimely “supplements” that materially change the theory or shore up a previously defective report. The estate neither showed substantial justification nor harmlessness. The panel emphasized the broad discretion district courts wield in policing these deadlines.

2. Excluding the cell-wall thickness opinion (Rule 702):

   The district court acted within its gatekeeping role. Dr. White:

   • Reviewed the wrong battery model’s online materials;
   • Did not measure the actual cell-wall thickness of Barrett’s cells despite having access to batteries;
   • Could not articulate a generally accepted or tested minimum-thickness standard (he floated 0.2 mm, then equivocated);
   • Did not account for the high-speed, multi-impact accident dynamics; and
   • Faced record evidence (from a CT measurement) that an actual cell’s wall measured 0.21 mm—exceeding his own proposed threshold.

   Given these deficiencies, the opinion would not assist the jury, lacked sufficient facts/data, did not rest on reliable principles/methods, and did not reflect a reliable application to the case facts. Exclusion was therefore well within the district court’s “broad discretion,” echoing Kilpatrick and Hughes.

3. Summary judgment on product claims (Florida law):

   For the cell-wall theory, exclusion left no admissible evidence of a defect/unreasonably dangerous condition—fatal under Nelson.

   For the intumescent-material theory, even accepting Dr. White’s reliability on the discrete point that intumescent material would slow or localize the fire, Florida’s causation element still required evidence that Barrett would have survived “but for” the absence of that material, proven as “more likely than not” (Gooding). The estate offered no such survival evidence—Dr. White opined only that the fire would have spread less, not that it would have been survivable. The panel rejected the invitation to apply the “substantial factor” test because the alleged defect was a dependent cause (it does not ignite fires; it merely mitigates spread), not an independently sufficient concurring cause. Thus, the ordinary but-for standard applied and was not met.

Impact

Although designated “Do Not Publish,” this opinion is a clear signal within the Eleventh Circuit—and a practical primer for Florida litigants—on both expert practice and causation in design-defect suits involving fire-spread mitigation.

• Expert practice and case management:
  • Courts will enforce expert-disclosure deadlines. A “supplement” cannot be used as a backdoor to debut new methodologies (e.g., for the first time claiming a differential diagnosis) or to change the certainty level after Daubert challenges.
  • Reliability scrutiny is exacting in highly technical cases. Opinions tethered to the wrong product, lacking measurements of the subject components, or detached from the accident’s actual dynamics will be excluded.
  • Engineering opinions must be testable, tied to data, and specify standards. Micron-scale assertions cannot rest on naked-eye observations.
• Florida causation in “fire-spread” and other mitigation-feature claims:
  • When the challenged design feature mitigates, rather than independently causes, harm (e.g., fire-retardant barriers, spread inhibitors, containment systems), Florida’s default “but-for” test generally governs factual causation.
  • Plaintiffs must adduce evidence that, more likely than not, the decedent would have survived if the mitigation had been present. Showing only that harm would have been less severe is insufficient without tying it to survival; Florida’s Gooding standard forecloses pure loss-of-chance recovery.
  • The “substantial factor” test remains a narrow exception for truly independent, sufficient concurrent causes. Plaintiffs should not expect to invoke it in typical “enhanced injury” or mitigation contexts absent proof that each cause, standing alone, would have produced the same injury.
• EV and battery litigation specifically:
  • Courts will expect accident-specific analysis: multi-impact dynamics, cell/module location, crush patterns, ignition sources, heat-release rates, occupant survivability timelines, and medical causation.
  • Patent disclosures or prior designs (e.g., earlier use of intumescent materials) may show feasibility, but they do not alone establish causation or defect without rigorous testing and survival analysis.

Complex Concepts Simplified

• Rule 26 expert disclosures vs. true “supplements”: An expert report must include every opinion, its bases, and key data by the court’s deadline. A true supplement corrects or completes information based on new facts learned later; it does not introduce a new methodology or change “maybe” to “to a reasonable degree of certainty” after a Daubert motion.
• Rule 37(c)(1) sanction: If you miss Rule 26 requirements, your expert cannot be used unless the failure is substantially justified or harmless. This often leads to exclusion and, if the opinion is essential, to summary judgment.
• Rule 702 reliability: Admissible expert testimony must (1) help the jury; (2) rely on sufficient facts or data; (3) use reliable methods; and (4) apply those methods reliably to the case facts. In engineering cases, this typically requires measurements, testing, literature support, and an accident-specific fit.
• Intumescent material: A fire-retardant material that expands when heated, sealing gaps and slowing fire spread. It is a mitigation feature—it does not prevent ignition but aims to prevent propagation.
• Florida “but-for” causation vs. “substantial factor”:
  • But-for: The injury would not have occurred without the defendant’s conduct; must be more likely than not.
  • Substantial factor: A limited doctrine for independent, sufficient concurrent causes (each alone could have caused the injury). It does not apply where the alleged defect merely depends on an initiating event to cause harm.
• Comparative fault (Fla. Stat. § 768.81): A jury apportions fault among all persons responsible; damages are reduced accordingly. Here, a $10.5M award was reduced to $105,000 after apportioning 90% to Barrett, 9% to James, and 1% to Tesla.

Practice Pointers

• For plaintiffs:
  • Lock down methodology in the initial expert report. Identify standards, quantify thresholds, and perform or commission measurements/tests on the actual components where feasible.
  • Develop accident-specific causation proof. In mitigation-feature claims, include survival analyses, time-to-flashover, occupant egress opportunities, medical causation, and “more likely than not” survival opinions.
  • Avoid reliance on “substantial factor” unless you can show truly independent, sufficient concurrent causes—an uncommon posture.
• For defendants:
  • Scrutinize the expert’s product identification, testing, and accident fit. Highlight failures to measure or model the actual product, and challenge speculative thresholds.
  • Press Rule 26/37 issues early; oppose late “supplements” that materially change the game. Cite Guevara to frame bolstering attempts as improper.
  • On causation, emphasize Florida’s Gooding requirement and distinguish dependent from concurring causes to keep the case within the but-for framework.

Conclusion

The Eleventh Circuit’s affirmance in Riley v. Tesla underscores two enduring themes in federal product litigation under Florida law. First, district courts retain broad discretion to enforce expert-disclosure deadlines and to exclude unreliable opinions under Rule 702—particularly when experts misidentify products, eschew measurements, or fail to tie theory to the accident’s real-world mechanics. Second, Florida’s but-for causation standard governs design-defect claims premised on mitigation features, absent truly independent concurring causes. Plaintiffs must marshal evidence that, more likely than not, the decedent would have survived but for the alleged design defect. Evidence that an intervening fire might have been less severe is not enough without a survival link.

As EV battery cases proliferate, Riley offers a roadmap: reliable, accident-specific expert work will decide admissibility and, often, outcome; and Florida’s causation law will continue to demand more than speculation about “what might have been.”

Disposition: Affirmed. (Per curiam; designated “Do Not Publish.”)