New England Patriots cornerbacks Stephon Gilmore and Malcolm Butler were among several players who took a knee during the playing of the national anthem before their game against the Houston Texans.
Patriots quarterback Tom Brady was seen locking one arm with wide receiver Phillip Dorsett.
More than a dozen Patriot players kneeled and locked arms. Fans began to boo the players before the anthem and continued after the anthem was over.
Earlier in the day, Patriots owner Robert Kraft said he was "deeply disappointed" with comments made by President Donald Trump on Friday.
Trump called for NFL players who did not stand for the anthem to be fired and fined for disrespecting the flag.