balk
A balk ordinarily results in an immediate dead ball and nullification of any pitch, and each runner is awarded one base. [1]
Games One of the spaces between the cushion and the balk line on a billiard table. [2]
A balk restricts the actions of the pitcher when there are runners on base. [3]
Baseball To make an illegal motion before pitching, allowing one or more base runners to advance one base. [2]
Most basically, a pitcher is restricted to a certain set of motions and one of two basic pitching positions before and during a pitch; if these are violated with a runner or runners on base, a balk is called. [4]
In general, a balk is called whenever a pitcher interrupts the pitching motion. [3]
In baseball, a pitcher may commit a number of illegal motions or actions which constitute a balk. [...] It should be noted that 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. [4]
Our pitcher was in the process of bringing his hands together in the stretch and backed off the rubber and threw to first. [...] If a pitcher balks but the batter puts the ball in play, this is *not* an option play. [...] Simply, if all of the runners and the batter advance at least one base, then the balk is ignored. [3]
If the pitcher should commit an act confusing to the batter with nobody on, or if he stops his delivery or otherwise violates because the batter steps out or otherwise acts confusingly, time is called and the play restarted without penalty (whether or not runners are on base). [1]
If even one runner does not advance, the pitch does not count, the batter returns to bat and all runners are given one base. [3]
A pitcher is allowed to feint toward third (or second) base, and then turn and throw or feint to first base if his pivot foot disengages the rubber after his initial feint. [1]
To stop short and refuse to go on: The horse balked at the jump. [2]
Sources:
[1] Balk - Wikipedia, the free encyclopedia
[2] balk - definition of balk by the Free Online Dictionary …
[3] What Is a Balk in Baseball?
[4] balk: Definition, Synonyms from Answers.com