Penalty Enforcement.

So I was working my first JV as Referee, I usually work Head Linesman. Here is the play we had last night that we seemed to get confused on.

A 2 and 5 on B's 35. A1 rolls right and throws pass down field that is intercepted by B80 at about B's 25. B80 returned the ball all the way for a TD. While B80 was returning the interception B73 hit A22 about 30yds behind the play before the ball crossed the goal line. My umpire threw a flag on the hit for what he called unsportsmanlike unnecessary roughness.

How would you enforce the penalty for that foul?