Boon, you're overcomplicating things. It should be kinda like Thunderdome - five aikidoka enter, one aikidoka leaves. The others leave a little later after they regain concious. Get a steel cage too.
Trust me, rules and referees can only get in the way of a good brawl. Stupid shodohai.
PS If I ever get off my lazy ass, I'll be using this as inspiration for the further Adventures of Shodothug!