by Josh Komon

Created on: October 10, 2009   Last Updated: October 11, 2009

Earned Run Average, often abbreviated ERA, is one of those baseball statistics that seems really simple, and for the most part, it is, but there is a component that can become very difficult to figure. ERA is to a pitcher what batting average is to a hitter. It represents the number of runs given up by the pitcher per nine innings, that were his fault. This is similar to BA in that BA is the number of hits per at-bat that were because of the actions of the hitters. Reaching on an error does not improve the batting average, and in fact, hurts it. From a pitcher's standpoint, giving up an error doesn't hurt the average, thought it doesn't help it either.

Quite simply, ERA is calculated like so: Add up all the earned runs given up, divide by the number of innings pitched. Multiply this answer by 9. That is the ERA. Here are two examples: A pitcher pitches six innings, and gives up two earned runs. Two divided by six is one-third. Multiply that by nine, and you get three. Therefore, that pitcher's ERA is 3.00. Next time out, that same pitcher pitches six more innings, and only gives up one more earned run. Now, the totals are 12 innings pitched, and 3 earned runs. 3 divided by 12 is one fourth. Multiply that by 9, and you get an ERA of 2.25.

If only it were always so simple. The hard part of ERA is determining what constitutes and earned run. Any runner that reaches base while that pitcher is pitching, who later scores counts as an earned run against that pitcher, with all the following exceptions:

1. A player who reaches on an error.

2. A player who scores as a result of an error, and would not have otherwise scored. (These account for many unearned runs, as an error that would have been the third out means every other run scored that inning is unearned.)

3. A player who scores as a result of a passed ball.

Earned runs that do count against a pitcher, but sometimes seem like they wouldn't occur in the following instances:

1. A player scores as the result of a wild pitch.

2. A player who was put on base by the pitcher in question, but scored while another pitcher was on the mound.

3. A player scores after reaching on a fielder's choice, which in turn put out an inherited runner.

A good rule of thumb is, whose fault was it that the run scored? Most of the time, if it's the pitcher, he gets charged with an earned run. After that, calculating the ERA is easy.

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