my first reaction is "Mother of Chr1st, I cant believe he/she did that" (Whistle Loud-n-hard)
Then it's "Ok, yeah, it happened, calm the f**k down" (a "take a breath" moment to ensure the players arent going to start brawling)
Then it's "OK, you're cool, make sure players dont retaliate"
Then it's "OK, now move the players away and deal with any injuries" (I am hoping the player is ok, but also hoping there's medical personel there so I can get a bit more chillaxed and talk to my ARs about the incident, though it's a pretty brief chat "I saw this, yes that's what I saw too, ok thanks"
Then it's a "remember, only talk to the captain, deal with the facts, and pull out ol' red". (No option, dangerous play, reckless, etc are phrases that come to mind).
Then get on with it til the end of the game, by which point my trustee #4 should have most of the paperwork filled for me to write the report!