If the rulebook you are looking at says that you must be looking at an older book. Out of the 2020 USSSA rulebook.
Sec 1. A legal pitch shall conform to the following:
A. Prior to the pitch, the pitcher shall take a position with their pivot foot in
contact with the pitcher's plate and their non-pivot foot in contact with or
behind the pitcher's plate. Both feet must be on the ground within or
partially within the 24-inch length of the pitcher's plate.
The hands must be apart.
The pitcher may not take the pitching position on the pitcher’s plate
without possession of the ball, and the pitcher may not simulate pitching
with or without the ball when near the pitcher’s plate.