earned run average

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A measure of a pitcher's performance obtained by dividing the total of earned runs allowed by the total of innings pitched and multiplying by nine.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun baseball a statistic in baseball which equals the number of earned runs allowed per nine innings pitched.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (baseball) a measure of a pitcher's effectiveness; calculated as the average number of earned runs allowed by the pitcher for every nine innings pitched