In baseball, allowing a designated hitter (DH) to bat for the pitcher creates the potential for moral hazard among pitchers, who may then hit more batters without the fear of retaliation by the opposing team. The use of the DH in only one of Major League Baseball's two leagues provides a natural experiment to test for the existence moral hazard in a controlled setting. We develop a new micro-level dataset of individual plate appearances, which allows us to control for detailed cost-benefit attributes that affect the decision calculus of the pitcher. We find that moral hazard explains 60 to 80 percent of the difference in hit batsmen between leagues and find evidence of direct retaliation against plunking pitchers.In other words, the DH rule not only does violence to the purity of the game, it also promotes violence on the field by removing disincentives to throwing pitches at batters.
The publication of the article raises once more the question of when that famous scholarly work, The Common Law Origins of the Infield Fly Rule, 123 U. Pa. L. Rev. 1474 (1975), will appear on the web.