Inside the Strike Zone: MLB Umpire Accuracy Factors (2024)

Undergraduates: Grant Danielson, Sophia Desai, Zach Ehmann, Opal Sharma, Ryan Smith

Faculty Advisor: Jonathan Jensen
Department: Exercise and Sport Science

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Major League Baseball (MLB) fans have long advocated for the use of an automated ball-strike system (ABS) to determine accurately whether a pitch is a ball or a strike in a game situation. This study examines how in-game factors influence the accuracy of an umpire's call in MLB games, aiming to evaluate the performance of umpires without ABS and determine the necessity of implementing such technology in MLB. The analysis collected data from Statcast via Pybaseball and considered every pitch in the 2023 regular MLB season. The data was used to perform a binary logistic regression of an indicator variable that of the call was correct or not on the count before each pitch, pitch movement, pitch speed, and a proxy variable for pressure. Our analysis revealed that while umpires made the correct call 92.6% of the time in the 2023 season, strikes, vertical movement, horizontal position, vertical position, speed, and pressure had a statistically significant effect on the umpire’s likelihood to make the correct call. Given the results of our study, future models should consider more nuanced variables or potential interaction effects to further analyze the feasibility of ABS in MLB.