"...The disrespectful display is irrelevant to the occasion...."

Nothing disrespectful exercising your first amendment rights, which is what the flag actually represents (the Constitution).  Since the NFL had no policy in place requiring how the players behave during the anthem, then they're doing nothing out of line.

Now, if you want disrespect, note how the flag is displayed during the anthem.  That's in direct violation of U.S. Code on respectful display of the flag.  Additionally, so is the flag on the players' helmets, as is the use of the flag's image in advertising.  Abide by the laws and fix that.

Personally, there's no relationship between a football game and the necessity to play the anthem and display the flag before, any more than we don't usually do it before a concert.  It isn't a government function.  It's a private entertainment event.  Don't expect anyone to act a certain way when there's no necessity for it in the first place.