Sidearm Deliveries Are Associated With Lower Shoulder and Elbow Injury Burden and a Favorable Performance Profile in Major League Baseball: A Cohort Study of 927 Pitchers (2020-2025)

Sidearm Deliveries Are Associated With Lower Shoulder and Elbow Injury Burden and a Favorable Performance Profile in Major League Baseball: A Cohort Study of 927 Pitchers (2020-2025). Dillon MR(1), Mastroianni MA(2), Frappa N(1), Manzi J(3), Fuller SI(4), Curtis W(2), Alexander FJ(2), Ablove R(4), Chalmers PN(5), Ahmad CS(2). BACKGROUND: Pitching-related shoulder and elbow injuries continue to rise in baseball despite workload restrictions and biomechanics-informed coaching. PURPOSE: To evaluate associations between arm slot and shoulder/elbow injured list (IL) time-loss burden and performance in Major League Baseball (MLB) pitchers. STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: Publicly available data were aggregated for 927 MLB pitchers who threw ≥1000 pitches during 2020 to 2025 and had arm angle data available from the MLB Hawk-Eye tracking system. Arm slot was defined as the throwing-arm angle relative to horizontal at ball release and averaged per pitcher (mean ± SD, 39.0°± 10.9°). Based on the distribution of arm slot values in the cohort, pitchers were categorized as sidearm (<33.5°; n = 255), three-quarters (33.5°-44.4°; n = 373), or overhand (>44.4°; n = 299). Primary outcomes were cumulative shoulder+elbow, shoulder, and elbow IL days accrued during the 2020 to 2025 study period. Performance outcomes included run prevention metrics, FanGraphs "plus" metrics (Stuff+ reflects pitch quality indexed to league average), strikeout and walk rates, hard-hit percentage (frequency of high-exit-velocity contact), and expected fielding independent pitching (xFIP; pitcher-controlled run prevention estimate). Group comparisons used 1-way analysis of variance with Tukey testing. Continuous associations with performance metrics reaching group-level significance were assessed with linear regression. Injury burden was modeled using negative binomial regression with log (total pitches) and percentage of games started as covariates; the primary analysis addition…