If Trump’s Twitter page within Twitter’s private enterprise is deemed a constitutionally protected free speech public forum as it influences public policy, then it follows that the nationally televised National Anthem within the NFL’s private enterprise is also a constitutionally protected free speech public forum as it also influences public policy.
The NFL is therefore violating the first amendment rights of these players with a public forum. Go ahead and start a class action lawsuit.
Private property rights further erode.
NFL’s new national anthem policy: Players must stand if on field but can opt to stay in locker room
Players refusing to stand for the national anthem had been a flashpoint for the league since Colin Kaepernick, then San Francisco’s quarterback, first began kneeling in 2016 to protest the treatment of African Americans in the U.S.
https://www.latimes.com/sports/nfl/la-sp-nfl-national-anthem-20180523-story.html