Revenge or Gratitude? Major League Baseball Pitchers' Performance against Previous Teams.

Professional athletes often change teams throughout the course of their careers. A common belief in sport is that players desire to have exceptionally better performances against teams that they have previously played for. The purpose of the current study was to investigate if there is support for the belief that athletes compete better against teams they have previously played for. We compared 229 major league baseball pitchers' career performance statistics to performance statistics against teams they have previously played for using paired sample t-tests. Our analysis of major league baseball pitchers indicated that they played significantly better against former teams as indicated by nine common pitcher performance metrics: Earned run average, opponents' batting average, walks plus hits per inning, opponents' on-base percentage, opponents' slugging average, opponents' on-base percentage plus slugging, strike-outs per nine innings pitched, walks per nine innings pitched, and hits per nine innings pitched. Evidence suggests that baseball pitchers perform better against teams they have previously played for compared against teams with no prior affiliation. Advanced sports analytics could help demonstrate psychological effects in sport. [ABSTRACT FROM AUTHOR]