I don’t follow American football, so I don’t know if Colin Kaepernick is a good quarterback or a bad quarterback. I don’t care. It took guts to not stand for the national anthem and he was right to do it.

Colin Kaepernick
Of course, it was for a good cause: to draw attention to police killings of black people. It’s a cause that should not be ignored and it is shocking that, despite the fact that it’s been going on for a long time, nothing still is being done.
Beyond that, though, I just don’t see why a sporting event should be a nationalist rally. In a stadium of 60-80,000 spectators, there are bound to be a few hundred who are not American, for starters.
You don’t sing the national anthem before the start of a rock concert, or before watching a film, so why before a football game? Does one have to be patriotic to enjoy a game?
I’m glad I no no longer live in the U.S. Although the Czech Republic is a sports mad country, you’re not likely to hear the national anthem except during international competitions, and then only if they win. You also don’t see the flag thrown in your face everywhere. They put little ones on the front of the trams on national holidays, but politicians don’t use massive ones as backdrops for their political rallies like they do in the U.S.
In fact, I think the U.S. is in a league of its own when it comes to flag worship. And it’s a big problem.