NFL teams will be fined if players kneel for the US national anthem under a new policy.
The American football league said players who do not stand for the Star-Spangled Banner can stay in the locker room until it has been performed.
The NFL also vowed to “impose appropriate discipline on league personnel who do not stand and show respect for the flag and the Anthem”.
Players said the protests were against police brutality of African Americans.
“It was unfortunate that on-field protests created a false perception among many that thousands of NFL players were unpatriotic,” said NFL Commissioner Roger Goodell in a statement accompanying Wednesday’s new policy.
“This is not and was never the case. This season, all league and team personnel shall stand and show respect for the flag and the Anthem.”
The policy includes the provision that clubs can develop their own rules – so long as they abide by the league’s directive – to handle players who do not wish to stand.
It does not state how much clubs will be fined should their athletes protest on the field, but gives them the option to impose penalties on any player who breaks the new rules.
The statement comes a day after NFL teams pledged $90m (£67m) towards social justice initiatives, under an agreement reached with all 32 teams in the league.
What’s the background?
The debate over the kneeling protests began in 2016, when San Francisco 49ers quarterback Colin Kaepernick refused to stand for the anthem.
Similar demonstrations spread across the league, where most players are African American.
Some kneeled, as Mr Kaepernick had done, while others linked arms to show solidarity for the movement.
President Donald Trump was highly critical of the protests, calling them “disgraceful” and unpatriotic. He also urged the players to be fired.
US Vice-President Mike Pence walked out of an NFL game because players from Mr Kaepernick’s team knelt during the anthem.