When government employees on government property at government events open to the public are trying to regulate how private citizens express themselves there are First Amendment issues.
The post I was responding to was making the blanket ask of "I want the Chief, these people don't want to let me have the Chief...First Amendment?" and not the Rosenstein situation, but let's game out that Rosenstein situation anyway.
Your above quote certainly sounds ominous! And drawn in the broadest possible terms, yes, there probably would be grounds for a speech complaint there. Fortunately, since this was a real thing that happened, we don't have to paint with broad brushes and can get specific.
Kent Brown, U of Illinois’ SID, acknowledged that in his Penny interview on 8/25/17 when he said that the DIA couldn’t stop fans from doing the “War Chant.” (Despite the fact that a DIA employee had done that very thing at a soccer game the day before.)
Kent is the SID, and not say, a guest blogger at Popehat, so I'm guessing this was mostly a combination of CYA and a matter of practical consideration - the "War Chant" boils down to people clapping in unison. How would that ever be policed in any meaningful way, even if one granted it was proper for the DIA to police it? On the other hand, if students at a soccer game were hurling racial epithets at one of the referees, surely you agree that they would either be asked to stop or removed from the premises, and the DIA would be justified in doing both?
I feel it's not a controversial statement to say in some circumstances, it would be reasonable for the DIA to intervene when someone is expressing themselves, regardless of the fact that they are a public entity. Watch a courtroom sometime - if someone is disruptive, actual armed agents of the state will remove that person from the proceedings. This bright line you're positing of "public employees can't do anything to private citizens trying to express themselves" doesn't really exist, at least not as you define it.
So when Rosenstein - a government employee on government property at a government sponsored event
It's also important to point out that while Rosenstein may be a public employee, he is
not employed by the DIA and he is not at the basketball game as an employee. Your setup of this scenario is so wildly broad that it would include a postal worker getting into a disagreement that escalates into shoving match with another person at the town tree-lighting ceremony at a public park.
Is that person guilty of assault? Maybe! Guilty of abridging someone's First Amendment rights? Laughably not, even though he would meet your criteria of being "a government employee on government property at a government sponsored event open to the public."
Oh, and about that last part...
events open to the public
Illinois basketball games are not "open to the public" - they are open to people that have tickets. And, as anyone who has purchased a ticket before understands, they are varying degrees of conditions that the buyer agrees to by the act of purchasing the ticket and entering the arena. DIA staff could tell someone wearing a "F*CK THE HOOSIERS" shirt (without the asterisk) to change/cover it or leave - that's not a First Amendment issue. Now, if UIPD hassle that same person for walking on the Quad with that shirt? Yeah, probably a different story. But that's not what we're dealing with here.
Rosenstein was arrested for exactly what he was guilty of - being a super creepy schlub. But it is likely a stretch to think that even a DIA staffer asking someone dressed in Chief regalia to leave the building would be considered a First Amendment issue, let alone this instance of some random professor - who is not working at the game or employed by the DIA - doing something in the same vein.
