The research, conducted at University of the South, in Sewanee, TN, suggests that National League pitchers, who must come up to bat, fear retaliation from the opposing pitcher. American League pitchers, who do not have to come to the plate, do not face the same fear.
In an attempt to boost interest in baseball in the early 1970s, the American League eliminated often-weak-hitting pitchers from AL batting lineups. In their place, "designated hitters" come to bat but do not play in the field. The National League has never adopted this rule, so pitchers always come to the plate in NL games.
However, one side effect of the designated hitter rule is that in the ensuing years the AL has generally had more hit batsmen than the NL. During the entirety of the DH era (1973-present), the hit-batsmen rate has been 15% higher in the AL than the NL.
While Major League baseball owners were angling for new players over the winter, mathematicians and economists were discussing the reasons why the designated hitter rule has led to more hit batsmen.
In a paper presented at the Joint Mathematics Meetings in Phoenix this January, a pair of researchers explored the reason for this phenomenon.
"There is no debate about the fact that the designated hitter rule is coincident with a higher rate of hit batsmen," said Doug Drinen, a mathematician at the University of the South in Tennessee, who co-authored the meeting paper with economist John-Charles Bradbury. "Rather, the debate is about why the rule causes the increase."
Two theories have emerged in the past few years. According to Bradbury, they both use the tools of economics, by weighing a team's "costs" of pitching inside to an opposing batter with the "benefits" it receives from that action.
One theory (the "moral hazard" theory) states that the NL's lower rate of hit batsmen is due--at least in part--to a higher "cost" for NL pitchers--a fear of retaliation when they step up to the plate. The competing theory--the "lineup composition" theory--states that AL's higher rate of hitting batters is due not to the lower cost of hitting a batter, but to the higher benefit of throwing "inside" pitches to the more slugger-concentrated AL lineups. Batters often have a harder time hitting inside pitches, but at the same time, pitchers increase their risks of hitting batters with those pitches. Striving to determine which factors are at work, Drinen and Bradbury performed a new, detailed analysis of Major League Baseball statistics from the years 1989-1992 as well as the 1969 and 1972-1974 seasons. Unlike past studies of this issue, which just analyzed the number of batters hit on a team per game, they analyzed individual plate appearances, so that they could look for evidence of retaliatory actions by pitchers in subsequent innings. The 1989-1992 seasons were the most recent seasons for which full data on individual plate appearances were currently available.
In their analysis, Drinen and Bradbury found strong evidence for the moral hazard theory. In particular, the researchers concluded that, during the time periods they studied, fear of retaliation was responsible for 60-80% of the difference in hit-batsmen rates between the two leagues.
"From a policy standpoint, no one disputes that eliminating the designated hitter rule would very likely lead to a decrease in hit batsmen," Drinen said.
Preprint of paper: