So the penalty statement in the latest online book is wrong? "PENALTY—10 yards. Penalties for Team A fouls behind the neutral zone are enforced from the previous spot. Safety if the foul occurs behind Team A’s goal line. [S43]."
Kalle, per 9-3-4, unless a defensive player is making an attempt to reach a runner, reach a ball loose ball, or ward off an opponent obviously attempting to block them, then they are bound by the same rules as offensive players with respect to using their hands and arms against an opponent. In the action described, B52 is doing none of those things, and is using his hands to “…illegally obstruct an opponent other than the runner.” The penalty is 10 yards (3 & 1, Basic Spot), plus an automatic first down.
It may also be an illegal block in the back, but, because this contact “…illegally obstruct(s) an opponent other than a runner…,” this action rises to the level of illegal use of hands/arms, which carries the automatic first down. This action is no different in effect than when a defensive player grasps an opponent - especially an eligible player - and restricts his free movement. A ‘pull and shoot’ is gets an automatic first down. A tackle of an offensive blocker to take him out of the play is an automatic first down. Equally, a block in the back simply to take a player out of the action - whether that is as a potential blocker for a runner or as a potential pass receiver - deserves the same penalty. 10 yards, and a first down.