• Earned runs figure into the pitcher's earned run average.pitcher in control image by CPonder from Fotolia.com
  
  Knowing how many earned runs a pitcher gives up is one of the factors in assessing a pitcher's talent. The Earned Run Average, or ERA, is calculated by taking the number of earned runs a pitcher has given up, divided by the number of innings pitched and multiplied by nine. This figures out the average number of earned runs given up per nine innings. Not all runs count as earned runs, however. Some runs are considered unearned runs.
  
  

Earned Run

• An earned run can be scored as long as the batter reaches base or scores without the aid of an error. This includes hits, walks, stolen bases or sacrifice fly balls. An earned run only counts against the pitcher's Earned Run Average, an unearned run does not. The official scorer for the game decides earned runs by thinking about the inning as if no errors were committed. If the scorer determines that an error caused a run to score, it will be deemed an unearned run.
  
  

Error

• If an error is committed by one of the fielders or the pitcher, and someone scores because of the error, it does not count as an earned run. This includes base runners who were able to advance a base because of an error, or who remained on a base only because of an error during an attempted fielder's choice. These runs are called unearned runs and are still tracked, but are discounted because they were not the pitcher's fault. If a run scores based on a wild pitch, it counts as an earned run, but a passed ball (a catcher's error) will count as an unearned run.
  
  

New Pitcher

• If a new pitcher enters a game and there are runners already on base, that pitcher is only responsible for the batters and runners he or she pitches to. This means that the previous pitcher, despite being removed from the game, will suffer giving up an earned run if one of the base runners scores, even though a new pitcher technically allowed the run to score. In the case that there are two base runners from the previous pitcher and the new pitcher gives up a home run to the next batter, the previous pitcher will be charged with two earned runs and the new pitcher will be charged with one earned run.