Zig - you have to kill a certain number of Purple Nine's (gang members with purple jackets on) in a limited time using only the uzi drive-by technique.

I found that if you stay in the area of the phone - other vehicles hit you a lot more, which obviously makes the mission much harder.

(with the phone on your right hand side) Drive down the road until it bends to the right and then just kill 9's on this stretch. I found there was generally more 9's here and less trouble from other vehicles.