Preventing wild pitches and avoiding passed balls. Although the pitcher has a responsibility to throw with reasonable accuracy, catchers must be mobile enough to catch (or block) errant pitches. By doing so, a catcher prevents baserunners from advancing while the loose ball is retrieved. An errant pitch that eludes the catcher and allows a baserunner to take one or more additional bases is called a wild pitch. (Techniques for blocking wild pitches are described in the previous section.) A pitched ball which would require only ordinary effort to be caught or blocked by the catcher—but is nonetheless misplayed, allowing a base runner to advance—is called a "passed ball".