Definition

A fielder is given an error if, in the judgment of the official scorer, he fails to convert an out on a play that an average fielder should have made. Fielders can also be given errors if they make a poor play that allows one or more runners to advance on the bases. A batter does not necessarily need to reach base for a fielder to be given an error. If he drops a foul ball that extends an at-bat, that fielder can also be assessed an error.

Defensive errors are a factor in some statistical equations. For instance, batters do not receive RBIs for any runs that would not have scored without the help of an error. And pitchers are not assessed any earned runs for runs that would not have scored without the error.