A ball that is misplayed or misthrown by a fielder is called an error. In baseball scoring, an error is a defensive mistake that allows a batter or baserunner to reach base, advance, or otherwise gain an advantage when an ordinary play should have been made successfully.
Errors can take several forms. A fielder might drop a catchable fly ball, mishandle a ground ball, or throw inaccurately to another base. The official scorer decides whether the play involved an error and which fielder should be charged. The judgment depends on whether a competent fielder at that position could reasonably have made the play.
An error is not the same as a hit. If a batter reaches because the defense failed to execute a routine play, the official scoring usually records an error rather than a base hit. Errors also affect earned-run calculations: a run made possible by an error may be unearned and excluded from a pitcher's earned-run total.