SET VS. WINDUP POSITION
Rules 5.07(a)(1), 5.07(a)(2):
The comment to Official Baseball Rule 5.07(a)(2) states, in part, that, “With a runner or runners on base, a pitcher will be presumed to be pitching from the Set Position if he stands with his pivot foot in contact with and parallel to the pitcher’s plate, and his other foot in front of the pitcher’s plate, unless he notifies the umpire that he will be pitching from the Windup Position under such circumstances prior to the beginning of an at-bat. A pitcher will be permitted to notify the umpire that he is pitching from the Windup Position within an at-bat only in the event of (i) a substitution by the offensive team; or (ii) immediately upon the advancement of one or more runners (i.e., after one or more base runners advance but before the delivery of the next pitch).”
Once the pitcher notifies the home plate umpire of his intention to pitch from the Windup, the umpire should call “Time”; the ball is dead; and the umpire should indicate to the other members of the crew and each Club that the pitcher has elected to pitch from the Windup.