NFL quarterback Colin Kaepernick called for further protests against racial injustice, after he received a prestigious award for his contributions to black history and culture.
Kaepernick, who has not played since the 2016 season, was the first player to kneel during the US national anthem.
Other players followed suit, leading to criticism from President Donald Trump.
"It is our duty to fight for them and we're going to continue to fight for them," said the 30-year-old.
Receiving the W.E.B. Du Bois Medal from Harvard University, he added: "I feel it's not only my responsibility but all of our responsibilities that as people who are in positions of privilege, in positions of power, we continue to fight for them, uplift them, empower them.
"If we don't, we become complicit in the problem."
Players who refused to stand during The Star-Spangled Banner have said the protests were against police brutality of African Americans and racial inequality.
Kaepernick has been without a team since he opted out of his contract with the San Francisco 49ers in March 2017.
He has filed a grievance against NFL team owners he claims conspired not to hire him because of his protests and has become the face of a new Nike advertising campaign.