In baseball, a pitcher may commit a number of illegal motions or actions which constitute a balk. When a balk occurs, immediate ensuing play is allowed to continue. If each baserunner advances one base safely, the infraction is ignored. Otherwise, the balk is called "no pitch" and each runner is awarded one base.
There are two motivations behind the balk rule. A pitcher is constrained to a certain set of motions prior to and during a pitch; if these are violated, a procedural balk will be called. Some pitching actions are illegally deceptive to runners or the batter; these punitive balks penalize such deception.
A balk call requires a high degree of judgment by the umpire; many times, umpires will take the intent of the pitcher and the effect of the questionable action into account when deciding whether to call a balk.
With a runner on base, it is a balk when the pitcher:
- switches his pitching stance from the windup position to the set position (or vice-versa) without properly disengaging the rubber;
- when going from the stretch to the set position, fails to make a complete stop with both hands together before beginning to pitch;
- throws from the rubber to a base without stepping toward (gaining distance in the direction of) that base;
- throws from the rubber to a base where there is no runner and no possibility of a play;
- steps or feints from the rubber to first base without completing the throw;
- throws from the rubber to the first baseman well off the base;
- pitches a quick return pitch, that is, pitches with the intent to catch the batter off-guard;
- pitches or mimics a part of his pitching motion while not in contact with the rubber;
- drops the ball while on the rubber;
- after a feint or throw to a base from the rubber, fails to disengage the rubber before reengaging and pitching;
- after beginning to pitch, interrupts his pitching motion;
- begins to pitch while the catcher is out of the catcher's box when giving an intentional walk;
- while pitching, removes his pivot foot from the pitching rubber, except to pivot;
- inordinantly delays the game;
- pitches while facing away from the batter;
- after bringing his hands togther on the rubber, separates them except in making a pitch or a throw; or
- stands on or astride the rubber without the ball, or mimics a pitch without the ball
A pitcher is allowed to jump with both feet, turn, and throw to a base toward which he turned. This is called a "jump turn", and is interpreted as a step and a throw from the rubber--even if the pitcher's foot physically came off the rubber.
A pitcher is allowed to feint toward third base, turn, and throw to second or first base, if his pivot foot disengages the rubber in his initial feint.
A pitcher is allowed to do almost anything once off the rubber. Once disengaged from the rubber, he may feint a throw, throw without stepping, or deceive runners as much as desired, as long he does not mimic a pitching motion.
A pitcher is allowed to feint to second or third base without throwing there.