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August 5, 2009

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by Shawn Hoffman

Imagine if the entire baseball blogosphere started using the original Runs Created formula—the one Bill James developed circa Off The Wall—as our primary way of valuing a player's offensive contribution. Forget run environments, linear weights, league adjustments, and all of the other things we've learned over the past thirty years; instead, for the sake of efficiency, we went back to (H + BB) * (TB) / (PA). Maybe it's not perfect, but hell, it's easy, and it's not like Willie Bloomquist is going to come out better than Adam Dunn.

Sounds ridiculous, right? But that's more or less what's happening right now with defense independent pitching stats. Quick, who's been better this year (numbers as of Tuesday afternoon):

Pitcher          K/9   BB/9   HR/9   GB%    ERA    FIP   SNWP
Jeff Niemann     5.7    3.1    0.8  40.7%  3.62   4.24   .567
Matt Garza       8.0    3.5    1.1  41.7%  3.69   4.23   .569

It looks pretty close. They play in the same ballpark, obviously, so we'll assume a similar run environment. Niemann and Garza have virtually identical ERAs, FIPs, and Support-Neutral Winning Percentages. Garza has a better K/BB ratio, but Niemann has allowed fewer home runs.

If you follow these things, you know where I'm going with this: HR/9—or HR/PA, depending on how you want to look at it—was one of Voros McCracken's original Three True Outcomes way back in 1999, and it's been treated as such ever since. But that didn't make sense then, and it doesn't make sense now—a pitcher's home run-rate isn't nearly as stable from year to year as his strikeout and walk rates, a fact that Voros himself noted in his early articles. Logically enough, when it's used as a major component of a defense-independent pitching stat, it makes that metric less stable as well.

This isn't new ground. There's been plenty of research done on the subject, and the explanation is pretty clear: a pitcher's HR/FB rate correlates about as well as his BABIP from year to year, especially after you adjust for park effects. Over the course of several years, there will be statistically significant differences between pitchers. But that simply doesn't manifest itself every single year, and if you're trying to evaluate a pitcher on a season-by-season basis, or in the middle of a season, it's probably better to just leave it out.