The purpose of this drill is to prevent timid hitters from backing out at the plate.
The timid little league batter always seems to assume that backing out will automatically prevent him from being hit by the pitch. He usually starts his getaway before he has any notion of where the pitch is really headed. I have had some success against this tendency by throwing behind the timid batter’s back. After all, he will get plenty of these pitches at the little league level, and you don’t want him backing into them and getting hurt.
Start out using spalding or tennis balls. At first, throw a lot of pitches behind him, then gradually decrease the frequency of these pitches as he starts to break the habit. Soon he will realize that he had better not back up until he sees where the ball is really going.
This will make him safer and more confident at the plate. And while he’s watching the ball more closely, he’s going to realize that he doesn’t have to hide from the good pitches, but can stay put and hit them.