Empowering the Jury: Third Circuit Clarifies When Expert Causation Testimony Is Unnecessary in Pennsylvania Products-Liability Litigation

I. Introduction

In Keith Slatowski v. Sig Sauer Inc., No. 24-1639 (3d Cir. Aug. 1, 2025), the United States Court of Appeals for the Third Circuit confronted a recurring tension in modern products-liability practice: How far may (or must) courts rely on expert testimony before allowing a lay jury to decide questions of causation?

The appellants, Keith and Bianca Cemini Slatowski, sued firearms manufacturer Sig Sauer after Agent Slatowski’s issued P320 pistol allegedly discharged without a trigger pull during routine training, striking him in the hip and thigh. The district court (E.D. Pa.) excluded portions of the plaintiffs’ expert opinions under Daubert and Federal Rule of Evidence 702, then entered summary judgment for Sig Sauer on the theory that Pennsylvania law required expert proof of specific causation.

Writing for a unanimous panel, Judge Bibas affirmed the Daubert exclusion but reversed summary judgment, holding that:

Although the proffered experts lacked reliable methodology to opine on the specific cause of this misfire, their testimony on general defectiveness of the P320 remained admissible; and
With that admissible evidence plus lay testimony, an ordinary jury is “well equipped” to decide causation without additional expert assistance under Pennsylvania law.

The opinion thus establishes a significant procedural precedent: Federal courts applying Pennsylvania products-liability law may deny causation experts yet still send the case to trial if the factual mosaic enables a lay finding without speculation.

II. Summary of the Judgment

Daubert Ruling: The district court correctly excluded the experts’ causation opinions because they were speculative and unsupported by scenario-specific testing.
Summary Judgment Reversed: Nevertheless, the Third Circuit held that Pennsylvania’s “functional” approach to expert necessity allows a jury to decide causation when lay testimony, physical exhibits, and admissible defect evidence suffice.
Remand: The case returns to the Eastern District of Pennsylvania for trial on design defect and causation with experts limited to defect testimony.

III. Detailed Analysis

A. Precedents Cited and Their Influence

1. Expert-necessity Cases

Reardon v. Meehan, 227 A.2d 667 (Pa. 1967) – Articulated the capability test: expert required only when jurors cannot comprehend the technical facts.
Storm v. Golden, 538 A.2d 61 (Pa. 1988) – Clarified “special skills and training” threshold.
Bialek v. Pittsburgh Brewing, 242 A.2d 231 (Pa. 1968) & Topelski v. University South Side Autos, 180 A.2d 414 (Pa. 1962) – Demonstrated instances where lay testimony, bolstered by limited expert background, sufficed for causation.
Oddi v. Ford, 234 F.3d 136 (3d Cir. 2000) – Exemplified scenarios demanding expert proof of complicated mechanical failure, used here as a contrast.

2. Products-liability Doctrine

Tincher v. Omega Flex, 104 A.3d 328 (Pa. 2014) & Sullivan v. Werner Co., 306 A.3d 846 (Pa. 2023) – Reaffirmed Pennsylvania’s risk-utility and consumer-expectations tests for design-defect liability, framing the substantive defect analysis.

3. Inter-Circuit Firearm Litigation

Davis v. Sig Sauer, Inc., 126 F.4th 1213 (6th Cir. 2025) – Similar P320 dispute; Sixth Circuit likewise permitted defect testimony while limiting causation evidence—cited approvingly.
Herman v. Sig Sauer, Inc., 2025 WL 1672350 (10th Cir.) – Non-precedential decision requiring expert causation testimony; distinguished on factual and state-law grounds.

B. Legal Reasoning of the Court

Daubert Analysis
- Rule 702 reliability demands that expert opinions be rooted in tested, replicable methodology, not speculation.
- Both experts failed to simulate holster conditions or measure required trigger pressure under those circumstances.
- Therefore, their conclusions on “what caused this shot” lacked the “real-world crucible of experimentation.”
Functional Test for Expert Necessity
- Under Pennsylvania precedent, the need for experts arises only when laypersons would otherwise speculate.
- The P320’s internal mechanics may be complex, but once experts explain those mechanics (defect evidence permitted), jurors can juxtapose that explanation with eyewitness accounts and physical exhibits (holster, pistol, alternative trigger).
- Hence, the absence of specific causation experts does not mandate judgment as a matter of law.
Summary-Judgment Error
- Fed. R. Civ. P. 56 permits summary judgment only where “no genuine dispute of material fact” exists.
- Because lay testimony (Agent Slatowski’s sworn statement that he never touched the trigger) plus defect evidence creates a triable issue, granting summary judgment was improper.

C. Potential Impact of the Judgment

Procedural Ripple Effect: District courts within the Third Circuit must now carefully distinguish between excluding unreliable expert opinions and dismissing a claim outright. The two inquiries are no longer conflated.
Elevated Role of Lay Evidence: Plaintiffs may survive summary judgment by combining limited expert testimony on background mechanics with credible eyewitness narratives.
Firearm-Design Litigation: The decision, alongside the Sixth Circuit’s Davis, increases the likelihood that P320 and similar misfire suits reach juries, potentially incentivizing design modifications (e.g., external safeties, tabbed triggers).
Expert-Economy Considerations: Parties may refine expert budgets, focusing on “design-defect” expertise while betting that juries can bridge the causation gap.
Influence Beyond Pennsylvania: Although grounded in Pennsylvania law, the functional approach mirrors many states’ doctrines; other circuits may find the reasoning persuasive when balancing Daubert rigor against the Seventh Amendment right to a jury trial.

IV. Complex Concepts Simplified

1. Firearm Terminology

Single-Action vs. Double-Action: Single-action triggers only release a pre-cocked striker; double-action triggers both cock and release the striker, requiring a longer, heavier pull.
External Safety: A manually engaged device (thumb lever or grip safety) that blocks the trigger until deactivated.
Tabbed Trigger: A small hinged tab on the face of the trigger that must be depressed before the main trigger moves, reducing inadvertent activation.
Internal Safeties: Mechanisms (e.g., striker locks, sear springs) that prevent discharge without a trigger pull but do not block the trigger itself.

2. Legal Concepts

Daubert Standard (Rule 702): Judges act as “gatekeepers” to ensure expert opinions are based on testable, peer-reviewed, reliably applied methodology.
Products-Liability vs. Negligence: In strict products liability, the “defect” substitutes for negligent conduct; causation and damages remain essential.
Summary Judgment: A procedural device that terminates a case before trial if no reasonable jury could find for the non-moving party.
General vs. Specific Causation: General – Can the product cause this type of harm? Specific – Did it cause this plaintiff’s harm on this occasion?

V. Conclusion

Slatowski v. Sig Sauer recalibrates the interplay between expert testimony and the jury’s fact-finding province in Pennsylvania products-liability actions. By affirming rigorous Daubert policing yet refusing to let that policing morph into a premature merits dismissal, the Third Circuit underscores a key principle: Courtroom science must be reliable, but jurors remain competent to connect the dots where the evidence—expert or lay—provides a reasonable pathway.

Going forward, litigants must craft dual strategies—one aimed at satisfying Rule 702 for defect analysis and another leveraging lay evidence for causation. Judges, in turn, must conduct a two-step inquiry: (1) vet experts; (2) independently assess whether the remaining record permits a non-speculative jury verdict. This decision thus reinforces both scientific rigor and the constitutional commitment to trial by jury, marking a pivotal development in the jurisprudence of expert evidence and products-liability litigation.