NEW YORK (AP) — A decade after he first took a knee during the national anthem, Colin Kaepernick will be publishing his life story.

The activist and former San Francisco 49ers quarterback has completed “The Perilous Fight,” to come out Sept. 15 through the Hachette Book Group imprint Legacy Lit. His memoir will come out almost exactly 10 years after he knelt before a preseason game, a protest against police violence and racial inequality that was emulated by some players and criticized by politicians, team owners and fans, some of whom booed him and burned his jersey.

Kaepernick, who has not played in the NFL since 2016, said in a statement that he wanted to offer context for what led to his taking a knee. Before that, he had remained seated during the anthem.

“People saw the moment. But they didn’t see the years that made it possible: the questions about who I was; the injustices I could no longer ignore; the voices of those who came before me that I carried into that stadium,” Kaepernick said in a statement released Tuesday. “That journey, from a Black kid navigating an identity the world didn’t always make space for, to an athlete who realized the game was bigger than football, shaped everything. When I took a knee, it wasn’t a sudden act.”

Legacy Lit is calling the book “equal parts memoir and manifesto,” tracing “the off-the-field battles that turned a single act of protest into a movement that changed American sports and culture forever.” Kaepernick is narrating the audio edition, produced and to be sold exclusively by Audible.

Kaepernick, 38, played six years for the 49ers and helped lead them to an appearance in the Super Bowl in 2013. Baltimore won the game 34-31.

Kaepernick has spoken out often on social issues, launched his own publishing imprint and co-written the picture story “We Are Free, You & Me” and the graphic novel “Change the Game.”