The NFHS Pitching regulations states (6-1-1) the pitcher shall not make a quick-pitch in an attempt to catch the batter off balance.  The penalty is an “Illegal Pitch”.  This being said it as an accepted practice to call “Time” prior to the pitch.  Disallowing the pitch by calling “Time” disallows the quick pitch and the penalty of the illegal pitch.  Stopping the quick pitch by calling time protects the batter that is off-balance and not ready to bat.  

If at all, prevent the quick pitch from occurring.  If the pitcher does continue to work quickly, after the umpire has stopped play then allow the pitch and award the illegal pitch penalty.  Remember the quick pitch puts the batter in danger of being in harm’s way by the batter not being prepared.  It is rare that an umpire will not stop play during the initial action of a quick pitch.