I thought there were NFL rules and game rules that pertained to the players standing on field during the playing of the national anthem.
"Throughout the period on game-day that a player is visible to the stadium and television audience (including in pregame warm-ups, in the bench area, and during postgame interviews in the locker room or on the field), players are prohibited from wearing, displaying, or otherwise conveying personal messages either in writing or illustration, unless such message has been approved in advance by the League office. Items to celebrate anniversaries or memorable events, or to honor or commemorate individuals, such as helmet decals, and arm bands and jersey patches on players’ uniforms, are prohibited unless approved in advance by the League office. All such items approved by the League office, if any, must relate to team or League events or personages. The League will not grant permission for any club or player to wear, display, or otherwise convey messages, through helmet decals, arm bands, jersey patches, or other items affixed to game uniforms or equipment, which relate to political activities or causes, other non-football events, causes or campaigns, or charitable causes or campaigns."
This clearly bars any political imagery on any part of the uniform. But kneeling during the Anthem is now a political statement, as is raising the fist (a revolutionary "black-power" symbol). And these do not fit into any of the banned categories. In my opinion, the black power raised fist is just as offensive as raising one's arm in a Nazi salute. I'm sure the NFL would come down hard on the Nazi salute, but hypocritically ignore the raised fist.
NFL Rule (unsportsmanlike conduct, edited):
There shall be no unsportsmanlike conduct. This applies to any act which is contrary to the generally understood principles of sportsmanship. Such acts specifically include, among others:
Using abusive, threatening, or insulting language or gestures to opponents, teammates, officials, or representatives of the League.
Using baiting or taunting acts or words that may engender ill will between teams.
Any violent gesture, or an act that is sexually suggestive or offensive.
These rules don't cover the kinds of demonstrations under discussion, and it's not made clear that they apply prior to or after the game.
My point is that the NFL needs to clarify these areas if they truly seek to get beyond this.