“So when is a question too complicated for the jury?” That is the question the Third Circuit sought to answer recently in Slatowski v. Sig Sauer, Inc., ___ F. 4th ___, 2025 WL 2178533 (3d Cir. 2025), reversing a district court’s grant of summary judgment despite affirming its exclusion of the plaintiff’s causation experts. Ironically, the Third Circuit’s analysis of when an expert opinion is required is itself so nuanced that it may require expert interpretation. Upon close inspection, the Slatowski panel’s holding is not nearly as broad as the headings might suggest.
Background
We summarized the district court’s analysis here. In brief, the plaintiff was a law enforcement officer whose pistol fired a round into his leg during a training exercise, allegedly without his finger on the trigger. He sued the defendant gun manufacturer and alleged that the gun’s safety mechanism, specifically the lack of a tabbed trigger, rendered the design defective. While the district court did not take issue with the plaintiff’s experts’ design defect opinions, it excluded their causation opinions as speculative. Then, reasoning that expert testimony was required in order to establish causation due to the complexity of the mechanism, the district court granted the defendant’s motion for summary judgment.
Expert Testimony
On appeal, the Third Circuit first addressed whether the district court properly excluded the opinions of the plaintiff’s two expert witnesses: a gunsmith and a firearms instructor. The panel agreed the experts’ causation opinions were problematic. First, neither expert attempted to replicate or simulate the accident scenario. Instead, they relied on theoretical analysis and statistics about accidental discharges, rather than testing how a tabbed trigger would have performed in the plaintiff’s specific circumstances. The panel agreed these opinions as to whether or not the firearm could fire more easily were speculative at best. Thus, finding no abuse of discretion, the panel affirmed the exclusion of the experts’ causation opinions. The experts could testify about design defects, but not about causation.
Critically, while it did not frame its holding in these terms, the Third Circuit apparently contemplated the experts being allowed to discuss general causation and objected only to their specific causation opinions: “[The experts’] testimony is reliable about whether the [gun]’s design could have caused an accident, but not whether it did cause this accident.”
Summary Judgment
The panel next addressed the district court’s grant of summary judgment for the defendant, which was premised on the notion that the plaintiff needed, but lacked, expert causation testimony. The Third Circuit took a different view.
Applying Pennsylvania law, the Third Circuit explained that expert testimony is required only when the subject matter is so complex that jurors would be unable to comprehend it without additional assistance. The court drew on three lines of cases: (1) those requiring experts
“where the theory of harm is abstract or technical”; (2) those requiring experts “where something seems to have gone very wrong with machinery, but the plaintiff is not sure what”; and (3) those in which no expert testimony is needed, because “even though the subject matter is complex, lay testimony can tell the story of causation.”
The panel noted not only that the gun’s “design is technical and probably needs explaining,” but also that the plaintiff’s “theory of the case turns on how [the gun’s components] interact: that something compressed the trigger, releasing the safety lock, and then when he reached for the gun’s grip, the sear was dislodged, causing the gun to fire.” But, because the plaintiff’s experts “may explain how all these internal mechanisms work together . . . [t]he remaining causation question is not beyond the average juror.” As the panel noted, that question “turns on whether [the plaintiff] is telling the truth and remembers it accurately, whether something could have gotten into the holster, and whether a tabbed trigger might have stopped some debris or the holster itself from depressing the trigger.” With the benefit of the experts’ explanation of the gun’s components, the panel concluded that a jury could apply lay reasoning to the controlling facts. Thus, it reversed the grant of summary judgment.
Analysis
Two aspects of Slatowski render its holding narrower than a casual read might suggest. First, the panel did not actually contemplate jurors addressing causation without expert opinion. On the contrary, the panel assumed that experts would testify about the design of the gun as well as the design’s ability to cause an accident in the abstract — i.e., general causation. The only question that the panel allowed jurors to address without expert opinion was specific causation, and even then, it couched that allowance in the knowledge that jurors would be “armed with enough expert knowledge” to decide that question.
Second, Slatowski should not be far removed from its facts. The panel’s focus on the credibility of the plaintiff’s testimony as controlling the inquiry cannot be ignored. If the panel saw specific causation as turning on whether the plaintiff’s testimony was to be accepted, it is not altogether surprising that it believed a jury could make that assessment. The case-specific nature of Slatowski is further illustrated in how it distinguished the Tenth Circuit’s contrary holding in another case involving the same product and the same alleged injury; Slatowski observed that the plaintiff in that case had not offered testimony that required the sort of credibility assessment at issue in Slatowski.
Conclusion
The Slatowski panel urged readers: “Do not underestimate jurors. Pennsylvania law requires expert testimony for complicated questions beyond a jury’s knowledge. But not every hard question is too hard for the jury.” However, the controlling question in Slatowski does not appear to have been especially hard. Slatowski’s holding is perhaps best understood as reflecting that jurors, with the benefit of expert testimony on all complex aspects of a case, may decide issues that hinge solely on the credibility of a witness.
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