Result of the play is............????

[bigwhistle]

B1 is set to receive a punt. While the punt is in the air, B2 blocks A1 in the back. The force of this block causes A1 to bump into B1, who then muffs the punt. After the muff, A2 recovers the ball.

Should this be A's ball, or should there be offsetting fouls? In other words, the major question is whether or not the illegal block by B2 which caused A1 to interfere with the reception of the kick is a foul or not (NCAA). I can find references to similar plays on roughing the passer situations and roughing the kicker situations, but not on kick catch interference situations. If you have an answer please give appropriate rule.