Easy.
One, for people invoking the First Amendment, they should start with actually reading it. "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances."
I don't believe Congress, or any part of the government, has passed or even proposed a law to stop the players from kneeling. What I do love is that the people upset at those objecting the the kneeling wish those objecting would be quiet. "Freedom of speech" that protects the players kneeling also protects someone else saying they disagree, calling for someone to be fired, or even using slurs if they so desire. Funny thing about the 1st, it tends to be a double edged sword.
The 1st isn't as all encompassing as some may think. It only keeps the government from quashing your speech. It does not prevent repercussions of that speech.
EDIT: Oh, and because Montel seems to require it to have an opinion, I wear the uniform.