You're Hurting My Game: Lineup Protection and Injuries in Major League Baseball

Does lineup protection exist? Observers of baseball frequently invoke the idea of lineup protection in which a batter will walk less and hit for more power if he is followed in the batting order by a high-quality hitter. Previous attempts to measure protection in Major League Baseball have sometimes found evidence of lower walk rates but never an impact on power hitting. I argue that these efforts fail to uncover such evidence because lineups are selectively chosen by managers, introducing endogeneity bias into ordinary linear regression and batting split comparisons. To remedy this problem, I use injuries to batters' "protectors" as a natural experiment that quasi-randomly changes the level of protection received by batters. Using this approach, I find evidence that protected batters hit for more power, hitting 9.7 percent more extra-base hits if the protector's OPS is 100 points higher. These effects are strongest among 3rd hitters, who hit 26 percent more extra-base hits under the same scenario. Supporting the previous literature, I find that batters walk more, especially intentionally, when left unprotected.