President Trump has some advice for National Football League owners: Fire players who kneel during the national anthem. He's also encouraging fans to walk out in protest. And the president is bemoaning what he describes as a decline in violence in the sport. Several athletes, including a handful of NFL players, have refused to stand during The Star-Spangled Banner" to protest of the treatment of blacks by police. Quarterback Colin Kaepernick, who started the trend last year when he played for the San Francisco 49ers, hasn't been signed by an NFL team for this season. The NFL Players Association reacted to Mr. Trump's comments Saturday morning in a statement: "This union ... will never back down when it comes to constitutional rights of our players as citizens as well as their safety as men in a game that exposes them to great risks." During his campaign, Mr. Trump often expressed nostalgia for the "old days" - claiming, for example, that protesters at his rallies would have been carried out on stretchers back then. He recently suggested police officers should be rougher with criminals and shouldn't protect their heads when pushing them into squad cars. It's also not the first time he's raised the kneeling issue. Earlier this year he took credit for the fact that Kaepernick hadn't been signed.