What is Earned Run Average?
Earned Run Average = 9 * (Runs / Innings)
In baseball, earned run average (ERA) is the average number of runs a pitcher allows per nine innings. This stat is used as a measure of a pitcher's expected effectiveness since each game is nine innings. Runs scored as a result of an error by a fielder do not count. These are called unearned runs.
The Major League Baseball all-time record for a single-season ERA is by Dutch Leonard. In 1914, he pitched 224.2 innings and only allowed 24 earned runs for the Boston Red Sox. This equates to an ERA 0f 0.96.
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