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Baseball Hacks by Joseph Adler

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Measure Fielding with Linear Weights

Use fielding runs to measure a player’s defensive performance with the linear weights system.

Fielding runs (FR) is a formula for measuring a defense’s contribution compared to an average defense. FR is the fielding part of the linear weights system for measuring player contributions. It measures the number of runs that a defense prevented from scoring compared to the league average fielder.

The Formula

Computing FR is a little bit more complicated than computing some other formulas in this chapter. First, I will explain how the system works. Then, I’ll explain how to compute fielding runs in four steps.

Comparisons to league average for position

For each measurement (A, PO, DP, E, PB), we compare the total fielded by each player to the league average. We call the league averages the expected numbers.

Adjustment for time played

We adjust the expected amounts by the time each player fielded each position. Ideally, we would use the number of batters or balls in play. But we don’t know this information. We do know innings played in each position, so we will use that measurement instead.

Weight by impact and position

We weight the impact of each defensive statistic differently. Assists count more than putouts, double plays, and errors (assists count twice as much for infielders) because they are harder. All of those count more than passed balls (a catcher-only statistic that’s half the pitcher’s fault). Outfield assists count twice as much as infield ...

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