It is a Case Book play and it is in the "Fighting/Not Fighting Section." I agree with previous replies that it should be considered flagrant.
9.4.1 SITUATION D: After completing the catch, receiver A12's momentum carries him into B's team box, where nonplayer B44 pushes A12 into a bench. RULING: Nonplayer B44 is disqualified and a 15-yard penalty is assessed from the succeeding spot.