Your misconception there is you think street fighting is not a game. I mean yes anything could happen. And you could get any fighter up there on that roof top.
But honestly you probably won't. What you get is still a pretty insular environment with your martial art adapting to handle a relatively small gene pool of fighters.
Which is essentially how these boxing tents can go from town to town and not get killed by every hard man that comes along. These street fighters are still working within their own confines. In this case are limited by their training and their competition.
Oh, man. Tonight we had a new guy come into the gym who said he'd been in a few 'rough and tumbles.' His jab > haymaker combo wasn't bad at all, i'd say he could beat the crap out of someone, but he was out of breath after A MINUTE of light sparring... and he wasn't even getting hit back...