Stills' protest came after President Donald Trump accused players of disrespecting the American flag. He has kneeled during the 2016 and 2017 seasons, ESPN reported.
Trump responded with a tweet Monday morning, posting that the “NFL players are at it again.”
Numerous players from different teams, Trump tweeted, “Wanted to show their ‘outrage’ at something that most of them are unable to define.”
“They make a fortune doing what they love,” the President said, ending his tweet by telling players to “find another way to protest.”
“Stand proudly for your National Anthem or be Suspended Without Pay!” he tweeted.
Last month, the NFL suspended its new anthem policy, which mandated that players stay in the locker room if they wanted to protest, WFOR reported.
"There has been no change in the NFL's policy regarding the national anthem," league spokesman Brian McCarthy said in a statement issued Thursday night. "The anthem will continue to be played before every game, and all player and non-player personnel on the field at that time are expected to stand during the presentation of the flag and performance of the anthem. Personnel who do not wish to do so can choose to remain in the locker room.
"We remain committed to working with the players to identify solutions and to continue making progress on important social issues affecting our communities."
Wilson sat during the anthem once last season, refusing to stand while playing for the Kansas City Chiefs in Week 5 against the Houston Texans, the Herald reported.
Quarterback Colin Kaepernick, who first brought the protests to light when he took a knee in August 2016 while playing for the San Francisco 49ers, tweeted his support for Stills and Wilson.
In Seattle, three members of the Seahawks ran into the tunnel before the national anthem, according to The Associated Press.
Defensive linemen Branden Jackson and Quinton Jefferson, and offensive lineman Duane Brown exited the field after team introductions and before the anthem. They returned to the sideline after the anthem ended.
In Jacksonville, four Jaguars were not on the field when the anthem was played before their home game against New Orleans, ESPN reported. Linebacker Telvin Smith, cornerback Jalen Ramsey, running back Leonard Fournette and running back T.J. Weldon left the field and returned after the anthem.
At Baltimore, both teams stood, but Ravens linebacker Tim Williams stood alone in front of the bench with his back toward the field, ESPN reported.