The UK's bare knuckle fighting contest is underground and illegal, but there is a growing movement to try and get it legitimate. It certainly looks vicious and I'm sure its not to my taste. Some of these guys are getting on in age and fight youngsters 20 and more younger in years. It's interesting and I've heard the gypsies around the Fenlands sometimes do bare knuckle fights. Other travellers from all of the Isles come and invited guests. Its meant to be secretive, but everyone in the area gets to know the venues and the law does not intrude.
The above documentary is another venue from a person who wants to legitimise the sport. I think it would lose its appeal if it became regulated.