Unadopted CPSC Proposals and “Sight‑Unseen” Expert Opinions Are Out: Sixth Circuit Affirms Robust Rule 403/702 Gatekeeping and Harmless Rule 26 Violation in a Modified-ROV Products Trial

Case: Zachary Tyler Martin v. Polaris, Inc., Polaris Industries, Inc., and Polaris Sales, Inc. (6th Cir. No. 24-5852)

Court: U.S. Court of Appeals for the Sixth Circuit

Panel: Judges Griffin, Thapar (author), and Mathis

Date: November 4, 2025

Publication Status: Not Recommended for Publication

Introduction

This appeal arises from a severe injury suffered by Zachary Martin while riding as a passenger in a Polaris RZR recreational off-highway vehicle (ROV) that had been heavily modified with an aftermarket roll cage, lowered seats, and larger wheels/tires. During a high-speed maneuver, the vehicle tipped and rolled; Martin released the passenger hand-hold, was partially ejected, and his arm was trapped under the roll cage, leading to an amputation below the elbow.

Martin sued Polaris under Tennessee products-liability theories (strict liability, breach of warranty, negligent misrepresentation), seeking compensatory and punitive damages. After a six-day trial, a jury returned a defense verdict on all claims. Martin appealed three evidentiary rulings, each reviewed for abuse of discretion:

The exclusion under Rule 403 of evidence concerning the U.S. Consumer Product Safety Commission’s (CPSC) proposed but never-adopted ROV safety rules (including comments and trade-association materials);
The exclusion under Rule 702/Daubert of portions of Martin’s expert (Dr. Tyler Kress) opinions concerning defect/causation and safer alternative designs; and
The admission, despite a Rule 26(a)(2) disclosure lapse, of Polaris’s expert (Gary Rogers) testimony about scratch-mark analysis and the effect of aftermarket modifications—an omission the court deemed harmless under Howe factors.

The Sixth Circuit affirmed in full, holding that the district court stayed well within its broad discretion in managing prejudice, reliability, and disclosure issues in a modified-product design-defect trial governed by Tennessee law.

Summary of the Opinion

CPSC proposed-rulemaking evidence excluded (Rule 403): Even if minimally relevant to notice, the unadopted proposals’ probative value was substantially outweighed by unfair prejudice and risk of juror confusion about what rules actually applied when the product left Polaris’s control. The court emphasized the danger that jurors would conflate general risks of ROVs with proof that Polaris’s specific RZR model was unreasonably dangerous.
Plaintiff’s expert excluded in part (Rule 702): Dr. Kress’s defect/causation and alternative-design opinions lacked a reliable methodology and application. He did not inspect the heavily altered vehicle before opining; he failed to identify a specific defect; he offered general suggestions (nets, windows, wrist straps, different roll-cage designs) without testing, feasibility, or cost analysis; and his “review and analysis” approach amounted to “trust me.”
Defense expert’s undisclosed opinions admitted but harmless (Rule 26): Rogers’s scratch-mark analysis was not timely disclosed in a written report or supplement, violating Rule 26. But the violation was harmless under Howe because Rogers fully previewed the challenged opinions at his deposition weeks before trial, plaintiff did not object or move to exclude pretrial, and there was no trial disruption.

Analysis

Precedents Cited and Their Influence

Standard of review and harmless error: Burley v. Gagacki, 834 F.3d 606 (6th Cir. 2016), sets the abuse-of-discretion framework; Cummins v. BIC USA, Inc., 727 F.3d 506 (6th Cir. 2013), requires reversal only if an error affected the outcome.
Relevance and prejudice: Fed. R. Evid. 401–403; United States v. Householder, 137 F.4th 454 (6th Cir. 2025) (liberal relevance threshold); Old Chief v. United States, 519 U.S. 172 (1997), and United States v. Smith, 70 F.4th 348 (6th Cir. 2023), on unfair prejudice; United States v. Gibbs, 797 F.3d 416 (6th Cir. 2015), emphasizing district courts’ “wide latitude” in Rule 403 balancing; Vroman v. Sears, Roebuck & Co., 387 F.2d 732 (6th Cir. 1967), warning of the persuasive weight juries may improperly attribute to standards not in force.
Expert reliability: Fed. R. Evid. 702; Daubert v. Merrell Dow, 509 U.S. 579 (1993); Kumho Tire Co. v. Carmichael, 526 U.S. 137 (1999); United States v. Gissantaner, 990 F.3d 457 (6th Cir. 2021) (central role of reliable principles/methods and their reliable application); United States v. Sammons, 55 F.4th 1062 (6th Cir. 2022) (Daubert factors—testability, peer review, acceptance); In re Scrap Metal Antitrust Litigation, 527 F.3d 517 (6th Cir. 2008) (reliability, not correctness; but speculation is insufficient); Gales ex rel. Ranson v. Allenbrooke Nursing & Rehab. Ctr., LLC, 91 F.4th 433 (6th Cir. 2024) (no “take my word for it”).
Tennessee products liability and alternative designs: Tenn. Code Ann. §§ 29-28-104 (state-of-the-art/compliance relevance), -105(b) (unreasonably dangerous at time of sale), -108 (alteration); Brown v. Crown Equip. Corp., 181 S.W.3d 268 (Tenn. 2005) (trace injury to defect); Potter v. Ford Motor Co., 213 S.W.3d 264 (Tenn. Ct. App. 2006) (relevance of feasible alternatives); Johnson v. Manitowoc Boom Trucks, Inc., 484 F.3d 426 (6th Cir. 2007) (alternative designs must address safety/performance tradeoffs); Brown v. Raymond Corp., 432 F.3d 640 (6th Cir. 2005) (lack of testing/feasibility can doom expert proof).
Disclosure and harmlessness: Fed. R. Civ. P. 26(a)(2), (e); Howe v. City of Akron, 801 F.3d 718 (6th Cir. 2015) (five-factor harmlessness test); Thompson v. Doane Pet Care Co., 470 F.3d 1201 (6th Cir. 2006) (experts may elaborate at trial on disclosed opinions); RJ Control Consultants, Inc. v. Multiject, LLC, 100 F.4th 659 (6th Cir. 2024) (honest mistake does not excuse noncompliance, but harmlessness analysis applies); Bisig v. Time Warner Cable, Inc., 940 F.3d 205 (6th Cir. 2019) (importance factor cuts both ways); McHugh v. Olympia Ent., Inc., 37 F. App’x 730 (6th Cir. 2002) (Rule 26’s dual aims: narrow issues and eliminate surprise).

Legal Reasoning

1) Excluding unadopted CPSC rulemaking evidence (Rule 403)

Although the relevance threshold is “extremely liberal,” the district court found that the CPSC’s proposed but never-adopted ROV rules, commentary, and related association materials presented three distinct Rule 403 dangers that substantially outweighed any marginal probative value:

Regulatory confusion: Tennessee law evaluates danger and compliance with standards existing “at the time [the product] was placed on the market” (Tenn. Code Ann. §§ 29-28-104, -105(b)). Because no CPSC regulation ever applied to the RZR at issue, the court feared jurors would mistakenly hold Polaris to nonexistent standards.
Notice misdirection: The record suggested the CPSC materials spoke to classwide ROV risks rather than a defect in Polaris’s own RZR configuration. Under Tennessee law, what matters is whether the RZR was unreasonably dangerous (and whether the manufacturer had notice of that) when it left Polaris’s control—not whether ROVs as a category pose hazards.
Unfair prejudice: Jurors might infer Polaris ignored legal requirements, even though none existed—precisely the concern Vroman flagged regarding the “persuasive weight” juries may attach to standards not in force.

Balanced against those risks, the CPSC materials carried low probative value, particularly because they related at most to factory models, whereas Martin rode in a heavily modified vehicle. The court also allowed plaintiff to offer CPSC materials if tied to “actual notice” of a defect in this vehicle, but it found no adequate foundation for that limited use at trial. The Sixth Circuit deemed this careful calibration squarely within the district court’s discretion.

2) Excluding plaintiff’s expert opinions (Rule 702)

The court affirmed two Rule 702 rulings: exclusion of Dr. Kress’s defect/causation opinions and his alternative-design opinions, both for lack of a reliable methodology and application.

Defect/causation: Kress concluded the RZR was defective and caused Martin’s injury but did not examine the actual, heavily modified vehicle before opining. Tennessee law requires a plaintiff to trace injury to a defect present when the product left the manufacturer’s control, and product alterations can break causation (Tenn. Code Ann. § 29-28-108; Brown v. Crown). Without inspecting the altered RZR, Kress could not reliably link the injury to a defect attributable to Polaris. Methodologically, his “review and analysis” lacked testability, peer review, or any articulated standards—amounting to “trust me,” which Rule 702 rejects (Gales).
Alternative designs: Although feasible alternatives are relevant to “unreasonably dangerous,” Kress did not specify concrete designs or test them. References to nets, windows, wrist straps, or roll-cage changes were not developed with testing, feasibility, or cost/safety tradeoff analysis (see Johnson; Brown v. Raymond). He did not address visibility concerns or other tradeoffs for nets, and he offered no vehicle-specific application—especially problematic given the aftermarket modifications. “Common sense” is not a substitute for “reliable methods, reliably applied” (Sammons).

The Sixth Circuit also noted other courts have excluded Dr. Kress’s opinions as unreliable, underscoring that credentials alone do not satisfy Rule 702’s reliability prongs.

3) Admitting defense expert’s scratch-mark analysis despite Rule 26 lapse (harmlessness)

Rogers’s initial report did not include his scratch‑mark analysis or roll‑angle testing distinguishing the factory roll cage from the aftermarket cage on the accident vehicle. He disclosed those opinions in a deposition three weeks before trial but never served a written supplement. That violated Rule 26’s requirement to disclose “a complete statement of all opinions” in writing and to supplement in writing.

Even so, the Sixth Circuit upheld admission as harmless under Howe’s five factors:

Surprise: The deposition thoroughly previewed the scratch‑mark analysis. Plaintiff’s counsel did not object at the deposition and engaged the topic.
Ability to cure: Plaintiff could have objected pretrial, moved to exclude or strike, or prepared cross-examination—he did not. Cross-examination at trial further mitigated any surprise.
Trial disruption: None; the deposition disclosure allowed planning.
Importance: Important evidence cuts both ways. Here, plaintiff’s failure to act despite notice weighed against preclusion.
Explanation: Polaris’s reason (rebuttal to a late plaintiff supplement) did not excuse the lapse, but the lack of gamesmanship and the deposition notice muted the concern.

Four of five factors favored Polaris. Because the trial testimony mirrored the deposition and plaintiff had a fair chance to respond, the court found the Rule 26 violation harmless.

Impact

Rule 403 and unadopted agency proposals: Parties seeking to use unadopted CPSC proposals (or similar nonbinding, proposed standards) as notice or defect evidence face a high risk of exclusion where jurors might be misled into treating proposals as operative standards or conflating category-level hazards with a particular product’s defectiveness. Courts may still admit such materials for the limited purpose of proving actual notice of a defect in the specific product—if a proper foundation exists.
Rule 702 in modified-product cases: The decision underscores that when aftermarket alterations exist, plaintiffs’ experts generally must inspect and analyze the actual product and its modifications to opine on defect and causation. Generalized design critiques and wish lists of safety add-ons, without testing, feasibility, or tradeoff analysis, will not survive Daubert.
Alternative-design proof in Tennessee: The Sixth Circuit’s reliance on Johnson and Brown v. Raymond reaffirms that alternative designs must be specific, tested, and accompanied by discussion of safety/performance tradeoffs and cost/feasibility—not merely asserted as “common sense.”
Rule 26 practice: Written expert supplements remain mandatory. But where an opinion is fully previewed in a deposition and the opposing party neither objects nor moves pretrial to exclude, courts may find the omission harmless, particularly if there is no trial disruption and cross-examination is available. Litigators should preserve objections promptly and seek pretrial relief to avoid forfeiture arguments.
ROV litigation strategy: Manufacturers will emphasize modifications to sever causation and will leverage instructions/handholds and safety features actually provided. Plaintiffs should move early to inspect the exact vehicle and tailor expert analysis to the altered configuration. Attempting to bootstrap general agency concerns into product-specific defect proof is unlikely to succeed.
Persuasive, not binding: Although unpublished, the opinion provides useful guidance to district courts within the Sixth Circuit on managing jury prejudice, enforcing Daubert rigor in modified-product cases, and applying Howe’s harmlessness test to expert disclosure missteps.

Complex Concepts Simplified

Rule 403 (unfair prejudice): Even relevant evidence can be excluded if it risks making jurors decide on an improper basis—like assuming a company violated a law that did not exist. Courts weigh probative value against potential for confusion, misleading the jury, or unfair prejudice.
Rule 702/Daubert (expert reliability): An expert must do more than assert conclusions. The court looks for reliable methods (e.g., testing, peer review, accepted principles) and a reliable application of those methods to the specific facts. Experience helps, but experts must connect their experience to a transparent, case-specific analysis.
Alternative design: To prove a product was unreasonably dangerous, plaintiffs often show feasible safer designs. Courts look for specifics: what design, how it would work on this model, testing results, effects on performance and safety, and cost/feasibility.
Tennessee “alteration” principle: If a product is changed after it leaves the manufacturer’s control, that can break causation. Plaintiffs must show the harmful condition existed when the product left the manufacturer and that modifications did not cause the injury.
Rule 26 disclosures: Expert opinions must be disclosed in writing before trial, and additions require written supplements. If a party omits an opinion but the other side learns about it in a deposition well before trial and does not object or seek pretrial relief, a court may deem the omission harmless.

Conclusion

The Sixth Circuit’s decision reflects a disciplined approach to evidentiary gatekeeping in complex, modified-product litigation:

Unadopted regulatory proposals aimed at an entire product category are often more prejudicial than probative in a specific design-defect dispute, especially where state law focuses on conditions and standards at the time of sale and on the particular product’s configuration.
Daubert requires more than credentials and intuition—especially when the product is heavily modified. Without inspection, testing, and vehicle-specific analysis, defect and alternative-design opinions will likely be excluded.
Rule 26 remains a written-disclosure regime, but deposition previews can render a lapse harmless when the opponent had a fair opportunity to cure and trial proceeds without disruption.

For practitioners, the opinion is a reminder to: (1) ground design-defect theories in product-specific, tested methodology; (2) scrutinize the admissibility of proposed-but-unadopted regulatory materials; and (3) handle expert disclosures proactively—supplement in writing, and promptly object or move pretrial when the other side’s deposition reveals new opinions. While unpublished, the opinion is a cogent roadmap for trial courts balancing probative value, reliability, and fairness in modern products cases involving aftermarket modifications.