In baseball, a pitcher can commit illegal motions or actions that constitute a balk. Most of these violations involve pitchers pretending to pitch when they have no intention of doing so. In games played under the Official Baseball Rules that govern professional play in the United States and Canada, a balk results in a dead ball or delayed dead ball. In certain other circumstances, a balk may be wholly or partially disregarded. In the United States, under the National Federation of State High School Associations (NFHS Baseball Rules), a balk results in an immediate dead ball. In the event a balk is enforced, the pitch is generally (but not always) nullified, each runner is awarded one base, and the batter (generally) remains at bat with the previous count. The balk rule in Major League Baseball was introduced in 1898.
According to the Official Baseball Rules: "Umpires should bear in mind that the purpose of the balk rule is to prevent the pitcher from deliberately deceiving the base runner."
Balk actions
A pitcher is restricted to a certain set of motions and one of two basic pitching positions before and during a pitch. If these regulations are violated with one or more runners on base, an umpire may call a balk. The batter at home plate does not advance on a balk.
With a runner on base and the pitcher on or astride (with one leg on each side of) the rubber, under Official Baseball Rules, it is a balk when the pitcher: Switches pitching position from the windup to the set (or vice versa) without properly disengaging the rubber While on the rubber, makes a motion associated with a pitch and does not complete the delivery When pitching from the set position, fails to make a complete stop with his hands together before beginning to pitch Throws from the mound to a base without stepping toward (gaining distance in the direction of that base) Throws or feints a throw from the rubber to an unoccupied base, unless a play is imminent Steps or feints from the rubber to first or third base without completing the throw Delivers a quick return, a pitch thrown right after receiving the ball back, with intent to catch the batter off-guard Drops the ball while on the rubber, even if by accident, if the ball does not subsequently cross a foul line Unnecessarily delays the game Pitches while facing away from the batter After bringing his hands together on the rubber, separates them except in making a pitch or a throw Stands on or astride the rubber without the ball, or mimics a pitch without the ball Attempts to throw to a fielder in a spot not directly at a base Delivers a pitch during a squeeze play or a steal of home, if the catcher or some other player steps on or in front of home plate without possession of the ball, or touches the batter (or the bat). The ball is dead, the batter is awarded first base, the pitcher is charged with a balk, and the run scores With the addition of new pace-of-play rules introduced for the 2023 season, a pitcher is charged with a balk if he attempts a pickoff more than twice in a single at-bat without recording an out, and without the runner advancing.
Under NFHS Rules, a balk occurs when
There is any feinting toward the batter or first base, or any dropping of the ball (even though accidental) and the ball does not cross a foul line. The pitcher fails to step with the non-pivot foot directly toward a base (occupied or unoccupied) when throwing or feinting there in an attempt to put out, or drive back a runner; or throwing or feinting to any unoccupied base when it is not an attempt to put out or drive back a runner. An illegal pitch from any position. Failing to pitch to the batter in a continuous motion immediately after any movement of any part of the body such as he habitually uses in his delivery Taking a hand off the ball while in a set position (unless he pitches to the batter or throws toward a base or he steps toward and feints a throw to second or third base) Failing to pitch to the batter when the entire non-pivot foot passes behind the perpendicular plane of the back edge of the pitcher’s plate, except when feinting or throwing to second base in an attempt to put out a runner The pitcher makes a movement naturally associated with pitching and/or places his feet on the pitcher's plate without the ball.
The pitcher's acts of spitting on the ball, defacing or altering the ball, rubbing the ball on the clothing or body, or applying a foreign substance to the ball are not balks; however, it will result in the pitcher's ejection from the game if caught.