Trump blasts NFL players for kneeling during anthem: 'Stand proudly . or be suspended without pay' - ABC News
Rules for the national anthem differ across sports leagues - ESPN
Everything you need to know about NFL protests during the national anthem
NFL: Trump's toughest tweets knocking players for kneeling during national anthem
Goodell and N.F.L. Owners Break From Players on Anthem Kneeling Fight - The New York Times
NFL's national anthem policy will punish teams if players don't stand on sidelines
What the NFL rule book says about the national anthem
Trump says players who don't stand for anthem 'shouldn't be in the country' - ABC News
N.F.L. Anthem Policy Bound to Please Only the N.F.L. - The New York Times
Broncos players to stand together for national anthem Sunday vs. Raiders