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May 28, 2003

Lies, Damned Lies

Pitcher vs. Batter Matchups (Holes Part Deux)

by Nate Silver

In last week's Lies, Damned Lies, I reviewed Adam Dunn's major league career one plate appearance at a time, in order to determine how his performance changed when facing the same pitcher multiple times. For those of you who, like me, did some damage to your short-term memory over the long weekend, the idea was to discover whether, per Michael Lewis' discussion in Moneyball, Dunn is a hitter with a hole in his swing that gets continually more exploited in repeated trials.

In Dunn's case, the answer was a tentative "no", but a lot of people mailed me to ask that I broaden the scope of the analysis. As D.H. writes:

"I like your research, but my problem is that you've presented no baseline. It reminded me of a STATS Baseball Scoreboard article on whether Greg Maddux did better the more times he faced a particular batter because he's so "smart." The data showed that the hitters improved as time went on. But, like in your study, there was no baseline to compare against. Adam Dunn may show a drop-off the more he faces a particular pitcher, but maybe all players exhibit identical drops. Or, maybe all players exhibit more precipitous drops, and only the good ones (like Dunn) stick around because they only lose 20% of their value."

In other words, is there any systematic advantage to the pitcher or the hitter given repeated trials? Doesn't seem likely, I wrote back, not if the league is going to remain at some kind of equilibrium for very long. But D.H. is correct that it's a question that deserves further study, much like why on Earth I didn't wear sunscreen to the ballgame on Sunday.

As I mentioned in the Dunn piece, there is publicly available play-by-play data for each season from 2000-2002. In order to make sure that the players we're working with formed a closed system, I limited the analysis to players who made their major league debuts in 2000 or later. It was then possible to look at all possible 'pairings' of the batters and pitchers within this group--what happens when Billy Batter faces Pete Pitcher for the first time? For the fifth time? For the 20th time, after Bill Batter has dropped the -y from his name and grown a mustache, and Pete Pitcher is discovered to be three years older than listed and actually named Pedro Pichardo?

As a starting point, it's necessary to evaluate the batters and pitchers involved in the pairings to see how their quality compares to that of the league as a whole. Since players who have recently made their major league debuts are almost always young, we'd expect at least some distortions in their performance as a group.

In last week's piece, I introduced a method for adjusting for the strength of the pitchers that Dunn faced by evaluating their Batting Runs allowed per PA (an old Pete Palmer favorite). It's a straightforward way to generalize this approach for all the hitters in our sample, and to apply it to the pitcher side of our pairings as well.