Are fight clubs legal?

I would like to start a fight club, but there are, of course, some legal issues with such an organization. If it were done on my own private property, and all involved were there of their own free will, and all had agreed (possibly in binding contract form?) not to press charges, would it be legal? Illegality won't deter me, but knowing that I am at a slightly smaller risk of spending my life in prison would be comforting. I believe that a good brawl, without motivators like prizes or self defence or even winning can be very theraputic. Thank in advance for your answers