Association of the Universal Designated Hitter Rule With Changes to Injuries in Major League Baseball Pitchers.

Background: In 2022, Major League Baseball (MLB) implemented the universal designated hitter (DH) rule, thus allowing the pitcher to focus solely on defense while the DH, who bats for the pitcher, focuses solely on offense.

Purpose/hypothesis: The purpose of our study was to determine if implementation of the universal DH rule affected the incidence of injuries in MLB pitchers when compared with before implementation. It was hypothesized that the shift to the universal DH rule would be associated with a decrease in the rate of offense-related pitcher injuries.

Study design: Descriptive epidemiology study.

Methods: Using publicly available data, we identified injuries sustained by MLB pitchers during the 2021 (before the DH rule change) and 2022 (after the rule change) regular seasons. Pitchers placed on the injured list for non-gameplay related reasons were excluded. Statistical analysis was performed with the chi-square and independent t tests.

Results: The injury incidence rate decreased significantly from before to after the rule change for MLB pitchers overall (from 6.58 to 5.60 injuries/1000 athlete game-exposures [AGE]; P = .02) and for National League pitchers (from 7.62 to 6.26 injuries/1000 AGE; P = .04). No significant changes were seen in American League pitchers (P = .20). Injury locations that decreased from before to after the rule change were the thigh (from 0.52 to 0.21 injuries/1000 AGE; P = .003) and the hand/finger/wrist (from 0.63 to 0.30 injuries/1000 AGE; P = .01). Total time lost decreased from 9471 days before the rule change to 8857 days after the rule change (P = .00001).

Conclusion: Implementation of the universal DH rule was associated with a decrease in pitcher injuries overall and within the National League. Injuries to the thigh and hand/finger/wrist also decreased overall and within the National League. Furthermore, total days lost decreased from before to after the rule change. These findings may be due to the elimination of offensive gameplay requirements for pitchers, which highlights a positive consequence of the universal DH rule, but further studies are needed.