Insane and sick. Nothing to do with any sport with purpose and talent (like the art of boxing, or classical fight or some noble martial arts).
Not underestimating the athletic profile of the fighters, but sure as hell their brain is overestimated.
That's simply kicking someone harder than he kicks you, just brutality.
I'd like to know who's paying the costs of the obvious brain damages caused by long time practice of this obscenity