An error is a fielding or throwing mistake made by a player on defense that results in an extra baserunner who should have been out, or that allows existing runners to advance one or more bases.

More technically, a fielder is charged with an error when his a play either fails to result in an out or allows runners to advance when, in the opinion of the official scorer, an average fielder would have record the out or held the runners in place.

Most errors come when a fielder fails to catch a ball hit to or near him, but other errors can involve errant throws or simply mental miscues that result in inaction or the “wrong” action, thus allowing something good to happen for the team at bat.