let me adress the LLC issue since samuel browning has not.
I too practice law and focus heavily on asset protection. Depending on the state you are in, the rules will vary, however I can't imagine the LLC. covering you in this situation (throwdown) under any circumstances.
While courts are generally not going to "peirce the corporate veil" (meaning set aside or ignore the business corporation and allow you to be sued personally) they will if the corporation/LLC/LLP/FLP or other business organization is set up as a mere sham and an "alter ego" of the person.
One of the things that often protects you is the fact that you can demonstrate the corporation doing some form of business. For asset protection, investments, or management of funds you can squeeze this by even in the most questionable cases.
Let me ask you however what would forming an LLC do when the organizer or individual is merely forming it for the purpose of engaging in full-contact (or whatever level you agree on) sparring and cross training? There is no business here. You are merely trying to sheild yourself from an act undertaken when you are acting as an individual not an agent of the business entity, for an entity that will have trouble to show any business purpose or even produce a sham business purpose as an explanation.
Either way, even if the entity was valid, then they could still come after you personally saying you were the one sparring, or the organizer was the one managing and negligently not enforcing the rules. It is much more complex than this but this is the overview.
Also how many of you would actually shell out the few hundred (for a corporation) to potentially thousand + dollars (depending on your state) to form an LLC?
For that cost it would probably be cheaper to get insurance for the event, and insurance for this kind of thing is not cheap.