Assuming this is real and not staged with the hunter in on it . . .
If you believe the clown poses an immediate danger to you or to another, you have a responsibility to stop the threat. I would feel very bad if I displayed a weapon and the clown left, only to kill someone else. With a bow or with a firearm, unless you are a phenomenally irresponsible hunter, you are perfectly capable of reliably stopping this threat. If it is a real threat, why leave that danger out there to harm an innocent person?
I would shoot a rabid animal. I would shoot a predator endangering livestock, pets, or people. I am not sure why wearing a clown suit would make this dangerous predator different from other dangerous predators. I would not shoot him merely for waving a knife and acting menacing, but if he started to climb the tree stand, I would interpret that as a genuine and immediate danger to my life.
I’m with you. “Ability, opportunity, jeopardy” - of course, if he started to climb the tree stand, that’s the last thing he’d do.
The difficulty is the, shall we say, “Kim Jong Un” problem: what to do with some psychotic who has the ability to kill (spectacularly), opportunity (just a few seconds from delivering a lethal blow), but isn’t _quite_ across the line per jeopardy (isn’t climbing the tree stand, is sufficiently outside the 21 foot distance, etc) - he’s screwing with your mind just to screw with your mind, making you nervously evaluate where the line is and whether he’s crossed it justifying lethal force in response, with you both knowing he’s really not going to go there, except that he’s clearly deranged enough that he might.
My prime concern is that he’s going to great lengths to make the threat, is clearly deranged enough to follow through on it, and at some point you’re going to have to leave the area - at which point you’re more vulnerable, and probably don’t know where he is, subject to attack. ...but you don’t know.
SSS?