From last year's USSSA SP rulebook, (don't have a new one as I don't work SP):

"A ball is called by the umpire on each pitch not swung at by the batter if:

A. The pitched ball does not enter the strike zone.
B. The ball strikes the ground before passing completely over the plate or any part of the plate.

Effect: The pitched ball is dead after each ball, strike, or illegal pitcher action and must be returned immediately to the pitcher(unless an out occurs.)"