Tough one this, i am assuming you know the players is coming for you, and where he is coming from.
A mugger will usually run directly to your bunker, and (if he has any sense) wont be shooting at you, this gives you a big advantage that can be worked on.
Firstly act fast, every second you waste brings the mugger closer, pop out and in, after firing a string of balls while keeping your profile as small as possible to avoid being shot by the muggers back men. Since the guy is running straight at you, you should have no trouble hitting the runner, and your paint should easily break on him.
The problem, as people have already pointed out is that the player will probably go through with the mug anyway, be it as a result of adrenaline (always my excuse), or that he knows he can acheive his goal anyway.
This type of practice is very hard to marshall so you need to let the marshall know he was hit first, and if that means you have to paint the mugger with half a hopper of diablo then so be it.
After all, he was the one who got up and started running at you, what does he expect??