Colin Kaepernick left the NFL primarily because he became effectively blackballed by NFL team owners due to his protests against racial injustice and police brutality, which began with kneeling during the national anthem in 2016. Though he was still a capable player, his activism made him a financial and reputational liability in the eyes of some owners, leading to no team signing him after he opted out of his contract with the San Francisco 49ers in 2017. Kaepernick filed a grievance alleging collusion by NFL owners to keep him out of the league, which was settled privately in 2019. Attempts to return, including a workout arranged in 2021, did not result in any team signing him, partly due to sustained controversy and his time away from active play, which diminished his opportunities further.