Are you seriously going to throw at somebody when you're facing Randy Johnson?
--Curt Schilling (1)
In 1973, amid waning fan interest in baseball, the American League (AL) of Major League Baseball (MLB) instituted the designated hitter rule as an experiment. The stated goal of this rule change was to boost offensive output by increasing the talent pool of batters in the lineup. Traditionally, the competing teams field nine players who must play defense in the field and bat. Because of the importance of the pitcher, who is responsible for putting every ball in play, teams rely on pitching ability and ignore the hitting ability when choosing the pitcher in the lineup. Therefore, pitchers tend to be very poor hitters. By allowing teams to substitute a player of greater hitting ability known as the designated hitter (DH)--to bat for the pitcher the total offensive output increases. The experiment has since grown into an institution in the AL that differentiates it from the National League (NL), where all players must bat and play in the field.
The DH succeeded in turning the AL into the "power league" as intended, but an unintended consequence of the rule change is that the AL now has more batters hit by pitches than the NL. Traditional baseball lore holds that the lack of retaliatory punishment in the AL for hitting batters is the cause of this phenomenon. Veteran NL manager Dusty Baker describes the deterrent impact from a pitcher's point of view, "You can be bold in (the American) League and get away with [hitting batters]. It's different in our league where you have to hit." (2) Pitchers who do not have to bat (where they might face retaliation) are more willing to risk hitting batters than pitchers who do bat.
Given that the rules of the game in both leagues are identical except for the use of the DH, MLB created ideal conditions for a natural experiment to examine the impact of the DH on hit batters in a controlled setting. (3) Several economists have looked at the issue and found that there is a statistically significant relationship between the DH and hit batters. However, the reason for this difference is subject to much debate. It is possible for the hit batter differential to exist without the deterrent effect of retaliation. The rulebook punishment for hitting a batter--awarding the hit batter first base makes retaliatory enforcement costly for teams to employ. Pitchers are typically poor hitters who rarely reach base via hitting, while batters who are DHs are typically good hitters. The fewer hit batters in the NL may reflect the lineup composition, in which the pitcher must bat. NL teams will try to avoid plunking pitchers because they are relatively less likely to reach base than non-pitchers, while AL teams do not have this easy out in their batting lineups.
A problem with previous studies of the subject is their reliance on yearly aggregate data. Hit batters are rare events--approximately 1% of all plate appearances result in a hit batter--that occur in the course of game where other incentives are quite relevant. This means that identifying small changes in pitcher behavior from specific factors will be difficult to identify with aggregate data. Differentiating between the two competing explanations for the hit batter differential between leagues deterrence and lineup composition--requires micro-level data where we can control for in-game strategic incentives for hitting batters.
Using a unique play-by-play data set that allows us to control for specific factors that affect hit batters, we find that pitchers are still more likely to hit batters with a DH in the lineup than without. And though pitchers are hit more rarely than other players, pitchers do experience retaliation for hitting batters. Retaliation against pitchers who plunk batters, which was not found in earlier studies, is needed to generate an effective deterrent for pitchers in the NL. …