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Evaluating Pitching

Evaluating Batting | Evaluating Fielding


Wins and losses are the most common gauge of a pitcher's value, but they're a reflection of his team's accomplishment, not solely that of the pitcher himself. Indeed, American League President Ban Johnson so objected to counting individual wins and losses that he instructed league statisticians not to compile them from 1913 to 1919.

Wins and losses ascribe to one pitcher the credit for a win or fault for a loss despite the fact that at least eight of his teammates take part in determining the game's outcome. Moreover, the rules that assign wins and losses sometimes don't identify the pitcher who contributed the most to his team's victory.

A pitcher's task is not to win the game by himself, it's to do what he can to help his team win the game. The most effective way for a pitcher to do this is to prevent opponents from scoring runs. The statistic that best embodies this ability is earned-run average.

ERA has its flaws. A pitcher might be charged with earned runs allowed to score by a reliever's ineptitude. An official scorer's decision of whether a runner reached base on a hit or an error can change the whole complexion of an inning as far as earned runs are concerned. At least part of every pitcher's ERA consists of how solid the defense behind him is.

For the most part, though, ERA measures what we want to know: how well did the pitcher prevent opponents from scoring runs? ERA can be taken a step farther to determine what Pete Palmer calls pitching runs. Pitching runs are the number of runs the pitcher prevented or allowed compared to the league average.

For example, a pitcher with a 2.50 ERA in a league with a 4.50 ERA is "preventing" two runs a game assuming that a game consists of nine innings pitched:

4.50 league ERA - 2.50 pitcher's ERA = 2.00 runs prevented per game

If you take the pitcher's innings pitched and divide by nine, you can determine how many nine-inning "games" he pitched:

270 innings pitched / 9 = 30 games

Then multiply his runs prevented by his nine-inning games:

2.00 runs prevented per game * 30 games = 60 pitching runs

Thus, the pitcher prevented 60 runs compared to the league average.

Another adjustment has to be made to pitching runs: the effect of ballparks. A pitcher who pitches his home games in Dodger Stadium will benefit over a pitcher who pitches his home games in Coors Field. Consequently, pitching runs are adjusted for pitchers' park factor. Pitchers' park factor not only accounts for the pitcher's home ballpark, but also for all the ballparks where the pitcher's team played, and includes an adjustment for the fact that the pitcher does not face his own team's batters.

Pitchers' park factor is expressed so that 1.00 is average, above 1.00 represents a hitters' park, and below 1.00 represents a pitchers' park. For example, in 1998 Coors Field had a pitchers' park factor of 1.20, while Dodger Stadium had a pitchers' park factor of 0.91. The park factors used here are based on three-year averages provided by Total Baseball. To read more about park factor, consult the Glossary. Annual park factors are listed in the Standings and Team Pitching sections.

Park factor is applied to the pitching runs formula by adjusting the league ERA. For example, if the league ERA is 4.50, multiply by the park factor:

4.50 league ERA * 1.20 park factor = 5.40 adjusted ERA

Now calculate the hypothetical pitcher:

5.40 adjusted ERA - 2.50 pitcher's ERA = 2.90 runs prevented per game

270 innings pitched / 9 = 30 games

2.90 runs prevented per game * 30 games = 87 pitching runs

Obviously a 2.50 ERA in Coors Field is a stellar performance, and 87 pitching runs would be one of the best marks all time. Note also that a pitcher below the league average gets negative pitching runs, meaning he cost his team runs compared to the league average.

Pitching runs puts into perspective quality and quantity. For example, would you rather have a pitcher with a 2.50 ERA over 135 innings, or a pitcher with a 3.50 ERA over 270 innings? Assuming the league ERA is 4.50, who prevented more runs?

Here's the pitcher with a 2.50 ERA in 135 innings:

4.50 league ERA - 2.50 pitcher's ERA = 2.00 runs prevented per game

135 innings pitched / 9 = 15 games

2.00 runs prevented per game * 15 games = 30 pitching runs

Here's the pitcher with a 3.50 ERA in 270 innings:

4.50 league ERA - 3.50 pitcher's ERA = 1.00 runs prevented per game

270 innings pitching / 9 = 30 games

1.00 runs prevented per game * 30 games = 30 pitching runs

While one compiled a better ERA, and the other pitched twice as many innings, they were similarly valuable to their team in terms of runs prevented. Thus, pitching runs measures both how well and how much a pitcher contributes to his team.

Sources:

Glossary, Total Baseball, edited by John Thorn, Pete Palmer, Michael Gershman, and David Pietrusza (Sixth Edition, 1999).

The Hidden Game of Baseball, by John Thorn and Pete Palmer (1984).