You can't underestimate a street-banger. Granted they're generally imbecile and can't throw for more than a minute before they start to heave, but...
I've been in a couple fights outside of bars and in an UG fight club once (I was young, it was dumb, don't ask) and I found that even a skilled fighter can get rocked if he underestimates.
A banger will throw wild yes, but even a blind bird catches a worm occassionally. Deflect as many as you can, but at the same time backup in circles. Angle out not in and keep your inside facing him. It'll make him think you're retreating when in reality you're wasting his small energy reserve.
His stance will be piss-poor so you'll want to throw kicks on instinct when you see those huge holes, don't. A banger will try and grab your leg and if he succeeds, you'll have to take it to the ground. I always find bangers heave and sweat terribly on the ground. Its really gross. Just make him tire then come in with a few tight rapid combinations to make sure he's good and gassed out. Then blast him with a cross right in the face. Goodbye banger. Then run because most bangers' cronies have guns or knives.