It was only in the second preseason game that an NFL Network reporter, an employee of the league, noticed it and reported the story. Once it broke, https://www.cnn.com/2020/05/29/opinions/now-is-the-moment-to-sign-colin-kaepernick-lockhart/index.html
Kaepernick worked with a former Green Beret, Nate Boyer, to find a more acceptable way to protest, and the National Anthem kneel -- "taking a knee" -- was born.
That played out for the whole 2017 season. Some players joined Kaepernick, but by the end of the season, there were only a handful of players kneeling. But those protests started important discussions within the league, specifically involving Goodell, during the offseason. I participated in several long conference calls where the commissioner and leaders of the newly formed Players Coalition grappled with how to use the NFL's vast platform to promote racial justice in America.
The new season started with very productive dialogue and work proceeding between the players and the league. That all changed on a Friday night in Alabama at a rally for Republican Senate candidate Luther Strange, where President Donald Trump called for kneeling players to be fired.
NFL owners should respond to those players "taking a knee" (who were overwhelmingly black) by saying "Get that son of a bitch off the field right now, he's fired!" he told the crowd.
That one rally changed everything. Although Kaepernick had not been signed in the off season, players' protests to that point were primarily off the field -- not during the anthem or on the field during games. But starting the following Sunday, hundreds of players were now kneeling and a full-blown battle with the President was drawn.