Again, no complaints about racist fans before they were turned off by the anthem protests. Perhaps they aren't stark raving racists, but merely disagree with the manner of protest? Nah. Too complex for you.
And the second part is like saying the NFL nipped the Second Amendment in the bud by not allowing firearms in stadiums. The Bill of Rights restricts the government, not private entities.
What do you not understand? The player protests are about racism and police brutality, they are not about only the NFL fans that happen to be racists. How are you still so willfully ignorant to this fact?
The NFL isn't in violation of the 2nd amendment because the second amendment has only been interpreted to say that people have a right to own guns, not a right to carry guns wherever and however they want. Hence why both private and public enterprise is allowed to make rules or laws restricting the carrying of guns. If the 2nd amendment said I had a right to carry guns, I would be able to waltz on over to my local public high school with a gun on my hip and not be in violation of any laws.
By saying one is not allowed to make a statement, that is infringing on one's right to exercise free speech. One can't "legally" (in quotes since breaking an NFL rule isn't a violation of criminal law) exercise their right to exercise free speech if the rules forbid it. No one is legally allowed to deny one the ability to exercise free speech, but they can potentially be punished for it after the fact, rather it be criminal charges or whatever the private enterprise rules state, based on the content of that speech.
Much like gun ownership, no one can deny you the right to own a gun (unless you fall under one of the nine exemptions), but what you do with said gun can potentially violate laws and rules.
Lastly, private enterprise isn't exempt from the Constitution. Have you lost your damn mind?
For example, my employer, a private college, can't forbid me from praying in my office as that would be a violation of the first amendment which gives me the right to free exercise of religion. They can fire me for doing it after the fact (though they would very likely find themselves in court over it), but they can't forbid me from exercising the right.
And my employer, once again a private college, can't prevent our students from owning guns as that would be in violation of the 2nd amendment, which grants them the right to own guns. However, they can tell these students that they aren't allowed to carry the guns on campus.
Please try to make yourself more informed before arguing over the Constitution. You are making yourself look like a damn fool.