Does The Pitcher Have to Show The Ball????

[fastballb]

Many times this year umpires warned my pitchers that they must first show the ball to the batter before bringing the hands together(start with the ball on the hip they said)...
Then you can bring your hands together and start your pitching motion....NFHS rule (high school) I am yet to find this rule in the rulebook...I watched the USA team play a few days ago and Fernandez started with the ball behind her back the whole time(the batter never seen the ball) Other pitchers started with the ball in the glove and then brought the hands together(yet the batter never seen the ball).I think in ASA rules you can start you pre-motion with the ball behind your back, ball on your hip or leg, or ball already in the pitchers glove....But what are the rules for NFHS......Thanks..