ARTICLE 5.A block in the back (other than against the ball carrier) is illegal.
Exceptions:
5. When an eligible player behind the neutral zone pushes an opponent in the back above the waist to get to a forward pass (Rule 9-1-5 Exception 4).
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].