Looks like a violation of the 1st amendment to me?
Nope. A violation of 1st Amendment more closely looks like people being denied the right to accept an invitation to speak on campus, or being denied the right to have a pleasant night at the theater or restaurant with their family purely because they don't parrot the leftist line. Stuff like that.
A football organization setting the standards of what is expected of its employees/players is not only within the spirit of the Constitution, but in my opinion is the civic duty of management. And the football organization that chooses not to insult the majority of its fans and chooses not to set a terrible example for the kids it should be role models for will get the Good Housekeeping Stamp of Approval from tens of millions of us.
Those who don't will continue to earn contempt from us as well as lose advertisers, fans, and respect.