Rule sets / OBR / Disengagement Without Dropping Hands Balk
Disengagement Without Dropping Hands Balk
A pitcher must drop his hands to his sides when disengaging from the rubber.
Pitchers may disengage the rubber after taking their signs but may not step quickly onto the rubber and pitch. This may be judged a quick pitch by the umpire. When the pitcher disengages the rubber, he must drop his hands to his sides.
From the Windup Position, the pitcher may: (A) deliver the ball to the batter, or (B) step and throw to a base in an attempt to pick-off a runner, or (C) disengage the rubber (if he does he must drop his hand to his sides).
MLB Umpire Development Manual Authoritative interpretation
From the Windup or Set Position, a pitcher may not: 4. After disengaging the rubber, step back onto the rubber without first separating his hands and dropping them to his side.