[kentref]

Thanks for the clarification.
I see this as a fumble by A through B's end zone. B is awarded a new series on B's 20.
I'm not seeing why there should be any penalty on A. I suppose there could be a potential argument that B's action of "punching" the ball out of A's grasp should be an "illegal batting" penalty, but that action is legal with today's NFHS rules.
Another argument could be that B is supplying a new force into B's end zone, and that would result in a safety if the ball went through B's end zone.
Two potential arguments - but neither holds water in the context of the 2005 NFHS rules book.

Bottom line. The thought process needs to be that the ball is fumbled by A and it is A's fumble that puts the ball in and through B's end zone.