Pitch-Tracking Risk Factors and Warning Signs for Ulnar Collateral Ligament Injuries in Major League Baseball Pitchers

Abstract

Background:

Ulnar collateral ligament (UCL) injuries remain highly prevalent among baseball pitchers across all competitive levels, and there is a need for improved prevention and early detection. The increasing availability of advanced pitch-tracking data allows for granular evaluation of pitching changes that may precede UCL injury, offering a potential tool to identify risk factors and warning signs for injury.

Purpose:

To identify baseline pitch-tracking risk factors present in the preinjury season and to detect temporal warning signs of UCL injuries across sequential time windows, including the offseason and the outings immediately preceding injured list placement.

Study Design:

Case-control study; Level of evidence, 4.

Methods:

Major League Baseball (MLB) pitchers who met the inclusion criteria and underwent UCL surgery from 2021 to 2025 (n = 78) were matched 2 to 1 with controls (n = 156) by season, age, handedness, and workload. Fastball metrics were evaluated in 3 stages: (1) baseline differences in mean values and intra-outing variability during the full preinjury season; (2) within-pitcher changes across 3 defined intervals—late versus early preinjury season (ΔS1), early injury season versus late preinjury season (ΔOffseason), and immediately preinjury versus early injury season (ΔS2); and (3) linear trends over the final 5 outings before injury list placement. Mixed-effects models and paired comparisons assessed differences in mean values and intra-outing variability for 6 mechanical variables.

Results:

Injured pitchers showed greater variability in velocity (P = .012) and horizontal release position (P = .005) at baseline. A medial shift in release point was observed during ΔS1 (P < .001), followed by a lateral shift during ΔOffseason (P = .004). Extension variability increased in ΔS1 (P = .038) and significantly decreased across the offseason (P = .007). The spin rate rose significantly in ΔS2 (P = .019). Injured pitchers also demonstrated progressive velocity decline across their final 5 outings (P = .019); controls remained stable.

Conclusion:

This study identified distinct patterns of mechanical variability and short-term changes in fastball pitch-tracking metrics among MLB pitchers who ultimately underwent UCL surgery. Greater intra-outing variability in fastball velocity and horizontal release position emerged as potential risk factors, suggesting that less repeatable mechanics may be linked to injury. A cascade of warning signs also appeared across time points, including shifts in horizontal release point and fluctuations in extension variability which intensified before injured list placement, increased spin rate throughout the season, and a progressive decline in velocity in the final outings. By focusing on intra-pitcher variability within matched time windows, this analysis isolates short-term deviations from each pitcher's baseline. As pitch-tracking technologies advance, frameworks that benchmark a pitcher's current mechanics against their historical variability may enable earlier detection, workload adjustments, and injury prevention.