Of course it's up to the private owners....
The President of the USA should have kept his trap shut....
Why? He has the right to speak, too, and a responsibility to do so when he represents the highest authority of what those players are protesting.
Those players are protesting civil injustices towards black men, as example...that the police have killed over the decades who were unarmed, or carrying a toy gun etc etc etc, yet none have ever been punished...they are not protesting our anthem and flag...
The First Amendment is why our President, the head of our government, should not get involved and in the middle of this, period. It's the government that is restricted by our first amendment right, not the private owners and the owners should be able to make their own decisions without the government's top dog President calling mother's of player's bitches and without the President recommending they be fired if they don't stand up and sing praise to our nation/ our government as our government head snaps his fingers and wants them to....
He needs to shut up, and butt out...
If this is the case, the players are doing a piss poor job of getting their message out.
People are not reacting to what they are protesting about, they are reacting to the method of protest.
If players want to protest, let them walk around the field holding picket signs before the national anthem. Hell, let them refuse to play!!
As for the players' so-called First Amendment right, that is, simply, not applicable. Owners do not have to allow them to protest. Fans can punish owners for not stopping it, and they can punish players for what they perceive as disrespect for the flag, for the country, and for its veterans.
You can say that the fans are misinterpreting the message all you want - the fact is that, if the players want to get THEIR message across, they need to find another way. Nobody is listening to what the players claim they are saying - they are only reacting to what they see the players do.
As for the President -- he represents the people, and he is telling the NFL what the people are saying. Problem is - they aren't listening.