For that kind of behavior I would have used my .50 Beowulf. One shot splattered russian pos!
No joking. If I had been there, I would have ordered him to desist, and get on the ground and comply.
Had he continued (and you had a clear shot), or came my way, he would have been shot dead.
There is a precedent called disparity of force. And I would have used it.
Straight up head shot. Empty the cranial vault asap.