Penalize players for kneeling?

I saw this Twitter message from Donald J. Trump.

He asks whether the NFL player contract requires players to stand with the hand over their heart when the National Anthem is being played.

Then he suggests that players should be suspended for the season without pay if they kneel a second time.

Hmm. Interesting. That kind of reminds of when the boxing authorities denied the late Muhammad Ali the ability to make a living because he refused to enter the U.S. Army; he protested the Vietnam War on religious grounds.

The Supreme Court would rule later, unanimously, that Ali’s suspension from boxing was unconstitutional. He was being denied the right to protest the government.

Aren’t the players protesting local governments’ treatment of African-American offenders? Isn’t there a parallel here between today’s protests and the one that The Greatest made a couple of generations ago?