Quote Originally Posted by TaePo View Post
This would be one of the rare instances (when I was not sure who started what or if the person needing defended caused the use of deadly forced to be used against him, so that he had no right to a self-defense exception) where I would give up my element of surprise.

Command the combatants to cease/desist and drop all weapons. If there is no complying then I would consider use of deadly force until it totally stops. In the one what-if scenario where the disadvantaged man would then shoot the remaining assailant, then I would consider them next if they did not immediately stop after another warning.

This, anyway, is what I hope I would do to sort it out somewhat and stop further escalation without actually firing, if possible.

On the other hand, if I saw the whole thing and knew who started what, I would not give up the element of surprise by playing cop. Even if the 'victim' had started a deadly force scenario earlier, this is a separate incident and no one has a right to just kill someone when they see them again. This assumes they are not affecting an arrest as well which one would know if they saw the latest incident from the beginning.

IANAL and this is what I hope I could think through in a high intensity situation.
These are the two correct answers, and likely would save you from the chair if you intervened. At the least you can prove that you made every attempt to determine the situation and who or what was in what kind of danger, mortal or otherwise, and if there was a threat to you. If you command and one or both turn to you, then you are in mortal danger and you drop him, then wait for the other to decide if he wants to be dead too. If you command and they both comply, then you wait for the police to come sort it out. If you command and they don't stop nor come toward you, then it's cloudy, you are still not in imminent danger, and it's still not clear who the *assailant* is. I believe warning shots work too.

The law on this does appear clear that you need to be, as you said, affecting an arrest, i.e. make it clear to the *felon* that you intend to stop him from doing what he's doing and arrest him as a citizen.