"I am not going to stand up to show pride in a flag for a country that oppresses black people and people of color," he said. "To me, this is bigger than football and it would be selfish on my part to look the other way. There are bodies in the street and people getting paid leave and getting away with murder."
Kaepernick, who was making his return from injury Friday, maintains an active presence on social media and frequently retweets articles focused on the subject of police violence.
"I am not looking for approval," he added. "I have to stand up for people that are oppressed."
The NFL released a statement on Kaepernick's decision not to stand, saying: "Players are encouraged but not required to stand during the playing of the National Anthem."
ABC News has reached out to Kaepernick for comment.
This is not the first time an American athlete has weighed into the debate around racial oppression in America.
Following the police shooting deaths of Alton Sterling and Philando Castile in July, which were captured on video and spurred large protests across the country, New York Knicks forward Carmelo Anthony reached out to fellow athletes on social media, urging them to “step up and take charge” of the political environment.
“These politicians have to step up and fight for change. I’m calling for all my fellow ATHLETES to step up and take charge,” Anthony wrote in an Instagram post that featured an image from 1967 of top black athletes, including Jim Brown and Kareem Abdul-Jabbar, holding a news conference in support Muhammad Ali’s refusal to be drafted into the Army during the Vietnam War.
“Go to your local officials, leaders, congressman, assemblymen/assemblywoman and demand change. There’s NO more sitting back and being afraid of tackling and addressing political issues anymore. Those days are long gone. We have to step up and take charge. We can’t worry about what endorsements we gonna lose or [who’s] going to look at us crazy,” Anthony wrote.