From what i know, If its a clear threat to your life then yes you can shoot them, that's if you can get your gun out or pull it up to shoot them before they spray you , it's risky but if done its rewarding haha, I don't know about the knockout part tho buddy.Â
This would depend on the situation have you had any previous quality roleplay leading up to this scenario, if so yes but if someone was to just run up to you and say hands up or I will shoot you can't just straight out shoot him you would need to provide some sort of roleplay to the scenario yourself before shooting by for example running behind a vehicle and telling him to go away.
As said before you need to provide high quality roleplay to the scenario before acting back. Your best bet would be to either zip tie him and execute him or to shoot from the start rather then knocking him out to then shoot.
Be creative make sure that you always make a situation more fun and engaging.
AFAK there isn't anything wrong with this, but if it is only one guy and he hasn't said about other people it would be better to ziptie/allow him to get up and then roleplay with him from there(if he pulls his gun out then shoot him of course) but if it is a big gunfight with multiple people going at you then I don't see anything wrong with knocking out & then immediately shooting.Â
Always best to counter a threat with one of your own . if x happens to me or you do x then x will happen to you - unless of course they have already shot at you, in which case you can shoot back at them freely