Pain, to tell you the truth I'm not sure. Certainly we all have 1st amendment rights, but it's understood that employers do have the right to 'limit' what you can say on 'duty time'. If Kaepernick's 'employer' (the team or NFL) doesn't have a problem with him taking a knee, then that takes care of that issue. I'm sure the teams and the NFL wouldn't allow the Hitler salute, the middle finger, or for a player to engage in 'hate speech'. That would definitely get them fired or at least suspended. I think it says a lot that they seem to if not condone, at least not to condemn taking a knee.
Scrotus was way, way out of line advocating for teams to 'fire' players for their political beliefs. On one hand even the POTUS has 1st amendment rights, but most of them also have had a sense of time, place, and decorum and would never get involved in something like this, let alone make such inflammatory statements. But as we know, Scrotus appears to consider himself above the law and above the 'rules' that govern a democratic society. And he certainly knows how to play to his 'audience'.