I've been thinking about this very situation lately. I recently officiated an 8th grade boys game in which A1 saved a ball from going OOB by throwing it against B1 which caused the ball to go OOB off of B1. In this case the ball hit B1 square in the nads.
The rules prohibit pushing, hitting, holding, etc, etc, .. yet intentionally striking an opponent with the ball (even though it's not malicious) is permissible.
There is much more potential for injury when throwing a ball against another player than there is for say .... bobby pins in the hair. It just seems odd that this is allowed.
Just thinking out loud.