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May 18, 2006

Schrodinger's Bat

The Moral Hazards of the Hit Batsmen

by Dan Fox

"The designated hitter rule is like letting someone else take Wilt Chamberlain's free throws."
--Rick Wise (1974)

In the previous two weeks, we’ve been looking at historical hit by pitch rates and their trends, and investigating a variety of theories that have tried to explain the fluctuation of those rates. We’ve looked at a wide variety of theories that account for factors such as aluminum bats at the amateur level, changes in the strike zone, the increase in body armor, intimidation, retaliation, and even the win expectancy of the hit batsmen. While individual theories may lack explanatory power for a specific period of time, taken together they do provide insight into the sometimes opposing forces that underlie trends in baseball's complex competitive environment.

There is one trend, however, that we failed to discuss. So this week we’ll take a look at the difference in league rates of hit batsmen since the introduction of the designated hitter in 1973. This topic has been taken up before, so we’ll start by covering some of the old ground, and then hopefully add something new to the discussion.

Setting a Baseline

Before we discuss what the impact of the DH on HBP rates might be, let’s lay out the raw facts that have inspired so much conjecture. The following graph shows the percentage of AL hit batsmen per 1,000 plate appearances as opposed to the NL since the DH was adopted in the American League in 1973. The shaded line is a three-year moving average.