I am going to make a suggestion and say it should just be some kind of organized fights in someone's yard or basemant...
That's an interesting idea, and it would fit into what I was thinking.
I was going to have you start off with small fights, such as what you suggested, or it might even be based on whatever is going to go on with tavern brawls. Basically, something to get the PC noticed by people that recruit brawlers (basically it will be a hidden rank tracked by a global variable). You can work your way up to the next level of fights, whatever that might be. Eventually you will earn enough "rep" or whatever to be invited to fight in the arena. You'll still be a nobody, but at least it's a nobody that gets backdoor access to the arena. I want to make the arena similar to the one in Oblivion, but with bigger fights, more time spent in each tier, and more options. Maybe even give you actual teammates; who knows.
Well, that's just a basic idea, and obviously it needs polishing, but that's just the premise in my noggin at the moment.