https://www.npr.org/2018/09/09/646115651/the-veteran-and-nfl-player-who-advised-kaepernick-to-take-a-knee
So you probably know all this, but what you might not know is why Kaepernick started kneeling to begin with as opposed to something else, and that's where Nate Boyer comes in. He's a former active-duty Green Beret who had a stint in the NFL with the Seattle Seahawks. He initially advised Kaepernick to take a knee instead of sitting down during the anthem as a sign of respect.