The first line of defense is to be in Condition Yellow. If you have time to see an attack developing, you can formulate an appropriate response.
If, therefore you see an attack developing, or conditions for the assault are favorable, the first response should be to go somewhere else. As soon as possible.
There might, however, be times when you CAN'T run. What then?
First, channelize the approach. Loosely translated, this means to have the wall at your back. Make sure that you can't be blindsided.
Next, establish mentally your FPL. This means final protective line. In the military, this is the line your pour your defensive fire down as you prepare to get out of your position under fire.
In this instance, it means to establish the distance at which you will have your weapon at the ready, and where you have made the decision to shoot. And no, it's NOT seven yards. Even before that distance, they should be under gunpoint.
For a knife, bludgeon or other contact weapon, the distance should be at least 15 yards. For a gun, if they have it in their hand, and they are close enough for you to see that it's a gun.
Now, where does verbal judo come in?
This is where you are trying to talk your way out of a fight. But, verbal judo is really just the spoken manifestation of your presence. And, let's face it--if you are projecting the aura or demeanor of a sheep, you are much more likely to be attacked.
Remember the ounce of prevention--don't go into places where you might be involved in a fight. Don't get into piddling contests with people. If a disagreement turns into an argument, that's when you walk away.
"So, Mr. wise-guy, what if you HAVE to fight", you might ask.
1. Leave the threats for somewhere and someone else. Things you don't want to say are things like, "I'll hurt you"; "I'll kill you", "You don't wan't to screw with me", etc.
2. Make sure you achieve eye contact--steady eye contact. I have found that focusing on one pupil of the other's eye can be intimidating. But, MAKE SURE THAT THE HANDS THAT CAN KILL YOU ARE VISIBLE AT ALL TIMES.
3. Deliver your spoken in straight, emphatic tones. No, don't be a drill sergeant, and don't posture.
4. Radiate assurance and self confidence. The unspoken words and the physical presentation are what works for you here.
5. What has actually worked for me is this: "Stop. Leave me alone; I have nothing you want. Stay where you are--I'm leaving now." Then, a slow, observant retreat with their hands in sight.
6. Depending on the subject's demeanor, and number thereof, it might actually help to either:
a. Have your weapon in hand, in a pocket, or
b. Have your weapon about 1/4 free of the holster.
If you feel that you can talk your way out of a situation with a less menacing posture, that's good. Whatever works.
However, remember that it will only work if the BG gets the impression that they have backed a really big sharptoothed curly wolf into a corner, and that it would be a really good idea to NOT screw with him, but to let him go.