It's your choice, run away or shoot him as if you're doing a self defense, by meaning of that here's a simple example:
You're attending a meeting with your gang, a newbie comes to you and tries to knock you down with a Shotgun, you avoid it somehow, and kill him for your self-defense if needed.
Another example is that if you are in a smuggle, which is not started yet, some cop or a player comes near you, stays silent for a while, then shoots one of the smugglers. You shoot him in the head, or knock him down and kill him, or someone does it, is considered as self-defense.
If someone is deathmatching you, either you run away or try defending yourself, if you're in a somewhat serious matter.
Hope this helps.