United States Vice President Mike Pence left Sunday's game between the San Francisco 49ers and Indianapolis Colts at Lucas Oil Stadium after several San Francisco players knelt during the national anthem.
President Donald Trump tweeted that he directed Pence to take action if any players protested:
The relationship between the NFL and White House has been strained after Trump said during a speech in September that any NFL players who protested during the anthem should be kicked off the field or fired.
NFL players who chose to demonstrate during the anthem before Trump's controversial remarks maintained that they were protesting police brutality and racial discrimination and weren't disrespecting the flag or military.
Those protests began in August 2016 when former San Francisco 49ers quarterback Colin Kaepernick began sitting during the anthem in protest of racial inequality. He eventually transitioned to kneeling after speaking with former NFL player and Green Beret Nate Boyer, who suggested that kneeling would be more a more respectful gesture.
Kaepernick has remained unsigned by NFL teams this season.
A number of NFL players joined in those protests last season and continued to do so to open the 2017 campaign. Trump's comments triggered a leaguewide response from the NFL, however, with many teams locking arms during the anthem or remaining in the locker room entirely while the pregame ceremonies took place in Week 3.
Since those displays—which many NFL owners and the league office framed as shows of unity—several players have continued to demonstrate during the anthem.