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Baseball Hacks by Joseph Adler

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Measure Pitching with Linear Weights

Estimate the number of runs prevented by pitchers, compared to a league average player.

Pitching runs is a formula for measuring a pitcher’s contribution compared to an average pitcher. It’s another formula from Pete Palmer. It measures the number of runs that the pitcher prevented from scoring compared to the league average.

This formula is based on another popular formula: earned run average (ERA). This formula compares a player’s ERA to the league average ERA, yielding the difference in earned runs per nine innings pitched. This figure is then multiplied by innings pitched to yield a player’s contribution over a season. Finally, this total is adjusted to account for the number of runs, beyond average, credited to the defense.

(Incidentally, the original version of this formula measured only the difference between a player’s ERA and the league average ERA. But Pete Palmer later revised the formula to take into account the number of outs due to the defense. I like the improved formula much better, and I show how to compute only this version in this book.)

This statistic separates the pitcher’s performance from the defensive performance. To adjust a pitcher’s performance to his team’s defensive performance, the formula relies on the fielding runs formula (see “Measure Fielding with Linear Weights” [Hack #55] ). Here’s the formula for pitching runs:

	PR = IPOuts / 27 * (lgERA – ERA) – (IPOuts / tmIPOuts) * tmFR

In this equation, lgERA represents ...

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