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.
Most people wouldn’t have a chance taking on a 300 lb guy, necessitating the use of a gun to at least get them to stand down.