Main problem I see with this is the MMA practitioner did not wait for the black guy to actually put his hands on him or someone else prior to engaging him. The black guy was being verbal other than shoving the cardboard box.
Believe me, I am NOT siding with the black guy. He was in the wrong, but the MMA guy engaged too soon. If there are any lawsuits over this, I am afraid he may lose.
All of that being said, very nice takedown/dump on the head. The follow up ground and pound was likely unnecessary as he was likely out of the fight strictly from the slam.