Rule sets / OBR / Pitcher Removes Hand From Ball Balk
Pitcher Removes Hand From Ball Balk
If the pitcher removes his hand from the ball before beginning his delivery, it is a balk.
If there is a runner, or runners, it is a balk when the pitcher, after coming to a legal pitching position, removes one hand from the ball other than in an actual pitch, or in throwing to a base;
MLB Umpire Development Manual Authoritative interpretation
After coming to a legal pitching position (windup or set), if the pitcher removes one hand from the ball other than in an actual pitch or in throwing to a base, it is a balk. However, prior to assuming a legal pitching position (windup or Set Position) it is permissible for the pitcher to momentarily adjust the ball in his glove. In order for this to be allowed, the movement must be momentary in nature. If the pitcher has his hands together long enough that, in the judgement of the umpire, it appears that he actually come to a Set Position or has actually assumed the wind-up position, then should the pitcher separate his hands, a balk shall be called under Official Baseball Rules 6.02(a)(10).