I would not prosecute a MMA fighter for what is normal in the cage but I can think of several instances during MMA when it could easily be justified to prosecute an MMA fighter for something way out of the ordinary. Continuing with a submission hold after someone taps out to cause a serious injury, attacking an already unconscious fighter, or getting a weapon of some sort and returning to the ring. The day could come where a fighter loses it and delivers one more blow on someone who is obviously already knocked out and it could kill them. This is pretty extreme but I would see no choice but to prosecute that.
The hit taking Rudolph to the ground is something you see every Sunday in the NFL. The little scuffle between the two on the ground is again, very common. But swinging a helmet and hitting someone on the head that isnt wearing one is way way out of line and crosses every line there is. A 280 lb world class athlete swinging a football helmet and and unprotected head is something that could result in a life threatening injury and it should be treated as such. I realize that much of football is risking life threatening injury and the players on the field accept that but what happened last night was the most reckless attempt to do serious injury to someone I have ever seen on the field.