In reply to The Lemming:
There was a series about this on sky recently.
First round was a 6 man melee, 3 go through based on judges decision, 3 fight again. 1 goes through 2 go home.
The 4 are paired off and go 2 on 2. The winning 2 then go one on one against each other.
It was brutal and the level of effort that it takes is massive.