We investigate potential racial bias by Major League Baseball umpires. We do so in the context of the subjective decision as to whether a pitch is called a strike or a ball, using data from the 1989-2010 seasons. We find limited, and sometimes contradictory, evidence that umpires unduly favor or unjustly discriminate against players based on their race. Potential mitigating variables such as attendance, terminal pitch, the absolute score differential, and the presence of monitoring systems do not consistently interact with umpire/pitcher and umpire/hitter racial combinations. Most evidence that would first appear to support racially connected behaviors by umpires appears to vanish in three-way interaction models. Overall, our findings fall well short of convincing evidence for racial bias.
Hamrick, Jeff and Rasp, John, "The Connection Between Race and Called Strikes and Balls" (2015). Master of Science in Analytics (MSAN) Faculty Research. 4.