[CecilOne]

Without getting into details of this case or discussing why #3 would be my trigger, some thoughts:
What I have learned and done about spectator control is to tell the responsible coach that those spectators must be controlled or removed before the game will proceed; and stuck with it. It's probably the only ultimatum I use.
I would do everything possible, including removal of the coach, police presence, etc. to avoid punishing youth players with a forfeit for AA conduct.
I like what Andy and Dakota said:
" expect some griping on any close call, and may let a coach come out and discuss the call with me, but once the discussion is over and I ask him to return to the dugout, we're done."
"Coach comes out, "Can I have TIME, Blue?"... And then proceeds to have a quiet, polite discussion asking what I saw, etc. I explain what I saw. Coach continues, still one-on-one, business-like, "But didn't you see..." Things get to where I ask him to return to the dugout, but he is persistent - polite, but persistent. I'd continue to cut him some slack."
Am I a softy? No, I often lead the league in AA ejections.