I'm sure I'm the minority here, but I'm not flagging this coach, if I'm the wing. Yes he came out onto the field (after the play) - a total of maybe 1.5- 2 yards, if that. He's also very, very upset about something.* If we're going to flag him for being on the field, it's going to have to a lot more on the field than that for me personally - he didn't get in the wing's face, he had someone actively working to restrain him, and he can rant and rave all he wants - behind me. Now if it continues into the next play or three, I'll tell him that's enough, I heard you, and we escalate from there.
*While it in no way excuses him, it does provide context that he's not just jawing at the wing to be a turd butt or to get under his skin. Several times, where I've in a similar situation where the coach is very upset and I have no idea why, I'll straight up ask them, what did you see? And then they tell me, and if it's something I should have seen, I own it, if I know I didn't see it - 'Coach I just didn't see what you saw'. If it's something I wouldn't have been likely to see, I'll tell him I'll let X or Y official know what he (thinks he) saw, and that usually helps defuse the situation a little. Maybe D1 is different (actually, almost certainly so) but refusing to acknowledge him I don't think helped the situation.