I'd say if it was you're friend that was knocked out, then it could be seen as an attack on your group, and would give you the right to shoot him, but only if you are doing something with the friend, so say helping them sell drugs. For me, this would mean i'm involved in the situation too, and gives me the right to shoot (Personally, i'd still try to RP anyway). If you were just walking down Kavala street, and happen to see your friend being knocked out however, you should still have to initiate RP, as the situation isn't involved with you at all.