This sounds like a dare gone horribly wrong.
It looks like they are in a bar and the Cubs mascot is doing an appearance. Some bro decides it would be a good idea to take off the mascot’s head and well the mascot did not like that one bit and boom, he gets some jaw from him. Now this may or may not be an official mascot but honestly, it doesn’t matter all that much.
I bet that guy never does anything like that ever again.