Most private employers also can fire someone for their conduct when they're representing the company, off the clock. These guys are well known by the team that they play for, and therefore are representing the company at pretty much any time.
I REALLY don't give a rat's ass about them kneeling during the anthem, as they are paid entertainers, and if I was to watch football (I don't often) it would be to see the game, not what the players' views are.
It really saddens me that we are still even having the problems that are the root reasoning for the start of all of this. I saw some numbers the other day that something like 1.4% of the police involved shooting involved an unarmed black person. Ideally that would be a big for ZERO, but it's not realistic , just like zero% unemployment is not realistic.