Negative Eyewitness Testimony and Rule 59 Deference: Upholding Defense Verdicts in Negligence Per Se Lane-Change Cases

I. Introduction

In Masek v. Peterson (10th Cir. Aug. 6, 2026), Ashton Masek, a passenger, sued driver Paige Peterson in the District of Colorado (after removal from Colorado state court) for negligence and negligence per se arising from a Denver traffic accident. The case turned on whether Peterson violated a lane-change safety ordinance—Denver Revised Municipal Code § 54-234(1)—and whether the evidence at trial compelled a finding of negligence.

After a jury returned a defense verdict (finding injury but no negligence and no causation), Masek moved for a new trial under Federal Rule of Civil Procedure 59, arguing the verdict was against the great weight of the evidence. The district court denied the motion, and the Tenth Circuit affirmed.

II. Summary of the Opinion

The Tenth Circuit held that the district court did not abuse its discretion in denying a new trial because the defense verdict was not “clearly, decidedly, or overwhelmingly against the weight of the evidence.” The court emphasized that, on Rule 59 review, it views the trial evidence in the light most favorable to the verdict winner. It also underscored that the burden of persuasion remained with Masek to prove negligence, including any alleged ordinance violation.

III. Analysis

A. Precedents Cited

  • Mathis v. Huff & Puff Trucking, Inc., 787 F.3d 1297, 1309 (10th Cir. 2015)
    Provided the governing standard of review: denial of a motion for new trial is reviewed for abuse of discretion.
  • Queen v. TA Operating, LLC, 734 F.3d 1081, 1086 (10th Cir. 2013)
    Elaborated what constitutes abuse of discretion—clear error of judgment, exceeding permissible choice, arbitrariness, or a manifestly unreasonable judgment—framing the appellate court’s highly deferential posture.
  • Cavanaugh v. Woods Cross City, 718 F.3d 1244, 1250 (10th Cir. 2013)
    Supplied the demanding weight-of-the-evidence threshold: the verdict must be “clearly, decidedly, or overwhelmingly” against the evidence to justify a new trial.
  • Anaeme v. Diagnostek, Inc., 164 F.3d 1275, 1284 (10th Cir. 1999)
    Reinforced two key propositions applied here: (1) evidence is construed in the light most favorable to the prevailing party; and (2) the burden of persuasion stays with the plaintiff.
  • N.H. Ins. Co. v. TSG Ski & Golf, LLC, 128 F.4th 1337, 1344 (10th Cir. 2025)
    Restated the Erie principle: in diversity cases, federal courts apply the forum state’s substantive law—here, Colorado negligence principles (including the parties’ shared premise about negligence per se).

B. Legal Reasoning

The appellate court’s reasoning proceeds in three linked steps:

  1. Identify the controlling appellate posture (deference to the jury and district court).
    The court treated the Rule 59 denial as discretionary and reviewed it deferentially. It also applied the “clearly, decidedly, or overwhelmingly” standard, which is intentionally difficult for appellants to satisfy.
  2. Frame the substantive negligence-per-se issue as an evidentiary question for the jury.
    The jury was instructed that violating Denver Revised Municipal Code § 54-234(1) “constituted negligence.” The ordinance requires a driver to remain within a lane and not move lanes “until the driver has first ascertained that such movement can be made with safety.” Masek argued that the testimony of witness Addison Pierzina established a violation because Pierzina “did not see” Peterson check the adjacent lane.
  3. Explain why “I didn’t see it” did not compel a finding of violation.
    The court highlighted record facts supporting an inference that Pierzina’s attention was elsewhere “right before the accident” because she was “looking for a parking garage,” was unfamiliar with Denver, and did not see the other vehicle before impact. Viewed in the light most favorable to Peterson, those facts permitted the jury to conclude either:
    • Pierzina simply may not have observed Peterson’s safety check; and/or
    • Peterson did, in fact, ascertain safety consistent with Pierzina’s broader testimony describing Peterson as notably cautious.
    Critically, the court treated this as a burden-of-proof issue: Masek had to prove Peterson failed to ascertain safety; Peterson did not have to disprove it.

C. Impact

Although designated as a nonprecedential “Order and Judgment,” the decision offers practical guidance—especially in diversity auto cases—on how the Tenth Circuit evaluates Rule 59 weight-of-the-evidence challenges:

  • High bar to overturn a jury verdict via Rule 59. Parties appealing a denial of a new trial must confront two layers of deference: the jury’s role as factfinder and the district court’s discretion.
  • Negative observational testimony is often insufficient by itself. Testimony that a witness “didn’t see” a safety check does not necessarily prove the check did not occur, particularly where there is evidence the witness was distracted or not positioned to observe.
  • Negligence per se does not eliminate factual disputes about whether a violation occurred. Even where the legal consequence of a violation is fixed by instruction (violation “constituted negligence”), the predicate fact—whether the ordinance was violated—remains for the jury unless the evidence is one-sided.
  • Burden-of-persuasion framing matters at the close of evidence and on appeal. By emphasizing that Masek carried the burden to prove the violation, the opinion underscores that evidentiary gaps generally accrue against the plaintiff on post-verdict review.

IV. Complex Concepts Simplified

  • Negligence per se: A doctrine where violating a safety statute or ordinance can automatically satisfy the “breach” element of negligence. The plaintiff still must prove the violation occurred and that it caused damages (unless otherwise established).
  • Preponderance of the evidence: The civil standard of proof—more likely than not.
  • Rule 59 (new trial): A mechanism allowing a court to order a new trial for certain serious errors or when the verdict is against the weight of the evidence. It is not a redo simply because the losing party disagrees with the jury.
  • Abuse of discretion: A deferential appellate standard; the appellate court will not substitute its judgment merely because it might have ruled differently.
  • Diversity jurisdiction: Federal jurisdiction based on parties being citizens of different states and the amount in controversy exceeding $75,000; substantive state law applies.

V. Conclusion

Masek v. Peterson reinforces that, on a Rule 59 challenge, a plaintiff must do more than argue the jury “should have” credited a particular witness. Where the trial record supports reasonable inferences favoring the verdict winner—especially when the plaintiff’s proof depends on a witness’s failure to observe—the Tenth Circuit will not deem the verdict “clearly, decidedly, or overwhelmingly” against the evidence. The decision thus strengthens the practical lesson that negligence-per-se theories still require persuasive proof of the underlying violation, and that post-verdict relief is exceptional, not routine.