A balk in baseball is any action by the pitcher that violates the balk rule, which restricts the actions of the pitcher when there is at least one runner on base. The purpose of the balk rule is to protect the runner or runners from being deceived by the pitcher. For example, a pitcher cannot fake a pitch to the batter and instead throw the ball to a fielder to catch the runner off guard and potentially get the runner out.
When an umpire calls a balk, the ball usually is dead — which means that play immediately stops — and each runner advances one base. If, however, a pitch was thrown and the batter safely reaches first base through a hit, walk, error or otherwise and any runners safely advance at least one base, the balk is ignored, and play continues.
Here are many of the situations with one or more runners on base that would cause an umpire to call a balk:
The pitcher begins to make the motions typically associated with delivering a pitch but ceases during its delivery.When pitching from the “set” position, the pitcher does not come to a complete stop with his hands together in front of him.With his foot in contact with the pitching rubber, the pitcher fakes a throw to a base that is not occupied by a runner or fakes a throw to first base when it is occupied. Failing to complete a throw to first base after stepping toward the base or beginning to throw is ruled the same as faking a throw.While his foot is in contact with the pitching rubber, the pitcher throws to a base before or without stepping toward that base. The pitcher is permitted throw anywhere after stepping off the rubber.The pitcher makes a motion typically associated with his pitching motion but his foot is not touching the pitching rubber.When he does not possess the ball, the pitcher takes a stance astride the pitching rubber or with his foot in contact with the pitching rubber as though he has the ball.The pitcher makes a pitch before the batter has had sufficient time to get set in the batter’s box. The pitch would be called a “ball” if there were no runners on base.During a pitch, the ball slips out of the pitcher’s hand and crosses the foul line. This would be called a legal pitch and a “ball” if there were no runners on base.The pitcher delivers a pitch while he is not facing the batter.After pausing in the “set” position, the pitcher removes one hand from the ball or separates his hands without making a pitch or throw.The pitcher drops the ball on the pitcher’s mound while his foot is in contact with the pitching rubber.