THT:Colin Wyers: How well can we predict ERA?

Ability vs. Value

I have written at length before on the basic principles of ability (or true-talent level) verus value. There’s just one point I want to come around and reemphasize.

People tend to lean upon defense-independent estimates of pitching performance because they better predict future performance. (And, strictly speaking, they do.) This leads to a lot of fantastic confusion about the issue, with the argument being that if we want to look at past performance, we should ignore defense-independent measures and look at actual results.

This is wrong for the same reason that we look at a pitcher’s ERA instead of his win-loss record. A team does not consistently score the same amount of runs every game; thus it is possible for different pitchers, even different pitchers on the same team, to have vastly different amounts of run support. This is not a function of pitching, and the credit or blame for this should not righly be assigned to the pitcher.

It is the same with defensive support. Two pitchers, even two pitchers on the same team, cannot be presumed to have the same quality of support from their defense. Defense-independent pitching statistics seek to give us a way to compare pitchers with different defensive support fairly.

But for a value measure, we do not care if a result came from luck or skill. We attribute defensive performance to the defense, not because the pitcher has no control over it, but because someone else does have control over it.

Home runs, on the other hand, are not under the purvue of the defense (except for a few, very rare cases). Thus, for a value metric, it is appropriate to credit a pitcher for the precise number of home runs allowed, and not an estimate thereof.