If a player locks up his backside (doesn't get the backside rotation from his hips) and his hands catch up with his belt buckle, then the hands roll and don't stay palm up and palm down. When the hands roll the barrel picks up and can cause a hitter to top the ball.
I teach hitting middle pitches first, not outside. The reason is a middle pitch should be driven up the middle with the player getting to extension (in front, not at contact) and with balance. The outside pitch should have extension, but I don't care as much about balance. The inside pitch has balance but not extension.
The backside rotation is not as pronounced on the outside pitch. Many stills and videos of major league hitters hitting an outside pitch show the back foot facing the contact and not rotated to the pitcher. With the inside pitch, you sometimes see that, but good inside pitch hitters usually get the back foot (which is really the hips) through the ball.
Hope this helps. Try getting your friend to work his backside rotation more. See where his back foot is when he hits an inside pitch -- I'm betting it is locked up and there is little rotation.
