Dropping and disconnecting your hands from your shoulders during your load and swing, is one very good cause for pop ups. If my son sees a player dropping his hand he will throw high in the 1,2,3 strike zones areas. Its very hard for a hitter to catch up to the ball if they drop there hands and have to go back up to hit it. If they hit it, its usually is a pop up
drill
He got three out by throwing high change ups one time because it was the top of the batting order and he knew they would try to tee him up. Everything was pop ups, because they were swinging up on the ball. Nothing but change ups high. You should of heard the other coach squawk at his players.