True. I was just curious about their skill level for one, as well as a concern for safety. Sure, if there was an injury, calling 911 is an option, but at least in the UFC there are qualified people right there who can start treatment.
That's the most important thing, especially since time is always of the essence when it comes to more serious injuries.
I don't doubt that a well-organized tournament that involves full contact, can be safe enough. If anything, I stop by Shihan Yasuhiko Oyama's Knockdown tournament (as a spectator) each year, to watch some entertaining full contact matches.
In their case, though, they have trained medical staff on hand, with at least two licensed physicians that know what they are doing, during all phases of the tournament. The medical staff is well-equipped, and all competitors are health-screened.
Also, the matches are highly regulated. Finally, and equally important, the host (Oyama Shihan) is certainly sufficiently insured.
I strongly doubt that backyard tournaments have the resources to have this kind of care (both medical and legal) available in the event of a bad situation.
Yes it's true, that some people will say "I've been doing these (backyard) events for years, and nobody's ever gotten hurt!" However, those same people fail to realize, that eventually something will happen. After all, it's a contact sport, and you can't avoid the inevitable forever.