By definition, "to balk" means to stop, as at an obstacle, and refuse to proceed or to do something specified. In baseball, if a pitcher fails to complete his delivery once started, he is charged with a balk. The penalty for a balk is the base runner is awarded one base. Because of this, many base runners will try different strategies to make the pitcher balk.
One of the most common balks is when the pitcher fidgets or hesitates a bit. Once he is set, he is not allowed to move his shoulders, midsection, or legs unless he is going towards the plate. Often times, a pitcher will accidentally twitch his shoulder, or his knee will buckle. This is a balk, and the base runner will be awarded a base.
Another instance of a balk is when a pitcher performs a jump turn to make a pickoff to first base, but fails to throw the ball. If a base runner is stealing on first move, they will break when the pitcher jumps. Seeing this, the pitcher might panic and stop his throw to first. Once started, a pitcher must complete his jump turn by making the throw to first base.
A tactic used by base runners to make a pitcher balk is referred to as a big lead. When taking a big lead, a base runner will get an abnormally large lead, and once the pitcher comes set, he will attempt to steal second base. When this happens, an untrained infield may panic and yell different instructions to the pitcher. In this case, the pitcher might become startled and balk, resulting in the runner being put on second base.
Balks are not all bad. A good pitcher can use a balk to his advantage. When there is a runner on first base for a LHP, or a runner on third base for a RHP, the pitcher can "cheat" so to speak. When performing a pickoff to their respective bases, the pitcher is allowed a 45 degree angle for his step. A well trained pitcher can take a larger angle and fool the runner into thinking he is delivering a pitch to the plate, thus successfully picking the base runner off.
Balks can be a pitcher's worst nightmare, or a pitcher's best friend. Knowing the situations of when a balk might arise is a necessity for a good pitcher. Being able to use the "balk move" pickoff effectively can be a huge advantage for a pitcher.
For more ways to balk, check out Steven Ellis' article, Pitching Rules: 11 Different Ways a Pitcher Can Balk.
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