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November 11, 2007

Dropping In

Luck and Misfortune in Hitter Performance

by Jason Paré

In mid-August I was reading an article on a friend’s blog, in which he was reflecting on his preseason MLB award predictions and lamenting his pick of Chris B. Young for NL Rookie of the Year. Since I had hyped Young to him prior to the season, I felt it necessary to reply and defend my prognostication. Young was hitting just .235 at the time, but had 25 or so home runs, and had already built a reputation as a premier baserunner. In defense of my pick, I hastily replied, “He’s had bad luck. If you gave him even a league-average batting average on balls in play, he’d be hitting .270 and have All-Star overall numbers.”

Something about my statement, however, did not seem intuitively correct. I knew that multiplying a player’s balls in play total by a league-average BABIP and adding in the home runs was, at best, a brute force measure of what the player “should” be hitting, only slightly less variable than a player’s batting average itself. Still, I thought that with Young’s combination of power and speed, he should ideally be hitting with at least average luck on balls in play.

Thanks to Marc Normandin’s player profiles, most BP readers will be familiar with the concept that a player’s batting average is highly variable from year to year, compared with other important rate stats like isolated patience and isolated power.

The correlation reflected above supports the idea that that hitting for average is subject to great variance due to luck, whereas walk rate and hitting for power are less prone to variance unexplained by the player’s skillset.