I'll keep distance away from strangers. If a stranger steps in, I'll step back. To prevent a problem from happening is much easier than to let a problem to happen and then deal with it.
When I was young, there were some local gang members who approached me and I moved back. later on I knew them well and they asked me, "Why did you keep moving back when we tried to be friend with you?" I told them, "I didn't know you guys that well."
Is that self-defense lesson number 1 - remain safe distance?
Even in punching range, if you lean back and kick your leg out, your opponent's fist still cannot reach to your face.