In the US Army, taking a knee has a special connotation.
Before Sunday’s lineup of NFL games, over 100 players from several different teams took Colin Kaepernick’s lead from last year, and in silent protest took knees, locked arms, or stayed off the field entirely, before Sunday’s games. President Donald Trump responded with two tweets which together said, “If a player wants the privilege of making millions of dollars in the NFL, or other leagues, he or she should not be allowed to disrespect our Great American Flag (or Country) and should stand for the National Anthem. If not, YOU'RE FIRED. Find something else to do!”