Opposite Hand Advantage and the Overrepresentation of Left-Handed Players in Major League Baseball

It is generally believed that batters have an advantage when facing opposite-handed pitchers. While this opposite hand advantage is known to be ex ante, the performance of players is ex post, which contains information about their skill, hand (dis)advantage, and teams' recruiting strategies. Based on more than 1.3 million play-by-play data points in Major League Baseball from 2000 to 2012, we provide a quantitative estimate of the opposite hand advantage to show how it can be used as a determinant of the excess supply of left-handed players. The results indicate the opposite hand advantage accounts for about 7-15% of the ex post on-base plus slugging. Second, compared to average batters, marginal batters, both right-handed and left-handed, are more affected by the proportion of left-handed pitchers. Third, in terms of strategic advantage, 7.5% more left-handed batters should be employed in Major League.