I found this while Googling:

The NFL’s operations manual, which, unlike its rule book, is not available to the public, states:

“During the National Anthem, players on the field and bench area should stand at attention, face the flag, hold helmets in their left hand, and refrain from talking. The home team should ensure that the American flag is in good condition. It should be pointed out to players and coaches that we continue to be judged by the public in this area of respect for the flag and our country. Failure to be on the field by the start of the National Anthem may result in discipline, such as fines, suspensions, and/or the forfeiture of draft choice(s) for violations of the above, including first offenses.”

 Doesn't a player have to agree to abide by this in their contract?

Some high paid lawyer will argue that somehow. The NFL had a chance to show solidarity and integrity with kaepernick but failed. They should have let him go. This whole thing is an utter disgrace. The message the NFL is putting out is they are a greater power than the country. Better than the architects of this country. This country hasnt been at war since 9/11, only 10% of its population was. The NFL season was still going on. Athletes were stol getting paid. One athlete who heeded the call was Pat Tillman and he just didnt enlist he became an Army Ranger.
So these athletes who are saying they arent disrespecting the flag, vets etc. are absolutely WRONG! They arent police officers and many of them surely arent vets. Their message is not defined and so convoluted. They want to affect change? Put down the helmet and jersey - earn the badge or enlist. They just want the fruits that generations before them planted. These currwnt gen of high paid athletes are so disconnected from reality. They are heeding to the forces that want the US to fail.

They want to affect change? Put down the helmet and jersey - earn the badge or enlist.

I guess there really are people who think that way. Well, these two still managed to be friends, so...

I think the president should have stayed out of this one. While granted he isn't trying to use the government to enforce standing I don't think there is any way he could have came out on this issue that would have looked good for him. The NFL can handle it however they want. They are beholden to football fans, not the SCOTUS.