Originally Posted by mashnut
Careful about saying "palm down", your hand should stay on the plane of your throw. If you roll your palm down, that's still imparting OAT, just in the opposite direction of rolling your palm up.
And you need to specify if you are giving advice to a BH thrower or a FH thrower. Most forehand throwers should keep their palm up to keep from wrist roll-imparted OAT.