Whenever I see a post like this the first thing I think of is Troll. But since we are all friends on here that could never happen.
The best martial art is one you are trained in and have confidence in using. Most bruisers like you are talking about are going to stand up and throw until you fall down than they put the boots to you. So to stand up to someone you have to at least know how to take a punch then decide how you want to handle them, standing up or going to the ground. That being said the quickest way to that level is training at some gym that offers MMA.
Most guys like this usually back off if someone steps up and finds a way to disarm the situation comfortably. If that don't work 911 on a cell phone doesn't hurt either.
I was going to post a link to the same video as Safwan. It is cheesy but Bas is right on with what he is saying.
Just be careful, you never know when you step up if someone is going to be carrying a knife, or a gun and you have to be aware that in a tough neighborhood that is always a possibility.
Jamilla I have to get ready for work but I have some thoughts on your question and will post them later.