Three Seahawks left the field Thursday night while the National Anthem played at CenturyLink.
"There has been no change in the NFL's policy regarding the national anthem", league spokesman Brian McCarthy said.
A dozen games were played Thursday night.
The NFL's preseason kicked off last week with the Chicago Bears and Baltimore Ravens playing in the annual Hall of Fame Game. It happened before the Dolphins game against the Buccaneers, and former Chief Albert Wilson was one of the players who took a knee.
There were no other actions by either Seattle or Indianapolis players during the performance of anthem.
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The World Cup victor reportedly informed United bigwigs that he wanted to quit Old Trafford for Barcelona . Mourinho's blatant plea came amidst a groundswell of anger at the antics of the Man United board.
The Giants opened their preseason at home against the Cleveland Browns on Thursday, and Big Blue defensive lineman A.J. Francis raised his fist at the end of the anthem, NJ.com reported.
The Philadelphia Eagles' Malcolm Jenkins and De'Vante Bausby showed resistance to the ban before their game against the Pittsburgh Steelers by raising fists during the anthem, while their teammate Chris Long placed his hand on Jenkins' shoulder, according to Philadelphia-based sports reporter Les Bowen.
The NFL owners approved a new national anthem policy two months ago that requires players to stand if they are on the field during the anthem, and fines a team for any protest by its players.
The league and the players' union have yet to announce a policy for this season regarding demonstrations during the anthem after the league initially ordered everyone to stand on the sideline when "The Star-Spangled Banner" is played, or remain in the locker room.
Stills has routinely knelt for the anthem during his time with the team.