What must a pitcher ensure about their pivot foot during a legal set position?

In a legal set position, the requirement for the pivot foot is that it must be in a position such that only part of it is parallel to the pitcher's plate. This positioning allows for stability and control when delivering the pitch. By having part of the pivot foot parallel to the plate, the pitcher is maintaining balance and ensuring proper mechanics, which are critical for an effective pitch. This requirement also helps the umpire and observers make clear judgments regarding the legality of the pitch, as a correctly positioned pivot foot contributes to maintaining the pitcher's balance and control during the motion of throwing.

The other considerations regarding the pivot foot include that it should not be entirely behind the plate, angled towards home plate, or elevated off the ground, as these do not conform to the established rules regarding a legal set position.