This is a fair question, but the fact is these protests started as one thing and then became another. Many people rallying to both sides don't have a damn clue what it's about. Which is why I took the time to answer this question on Quora, reproduced in part below.

What is all this kneeling during the US national anthem about, what is it protesting?

Fair question. Sorry to say, most of the people in an uproar over it don’t have a damn clue. It takes too much time for them to grasp the details, so it is easier to make it an “us versus them” issue and line up on one side or the other. Politicians love that, as they can use it to fire up their base and to distract people from real issues.

The protest started out as one thing and then became another, but it takes a little time to fully understand that. I give the briefest summary I can below, with references, but first, here is what it is not about:

• It is not about protesting the national anthem.
• It is not about showing disrespect for those in the armed forces.
• It is not about disrespect for the flag or the country, but concerns about issues in a country represented by that flag.

Over a year ago, on August 14, 2017, professional football quarterback Colin Kaepernick sat quietly (he did not kneel at first) as the national anthem was played during a San Francisco 49ers preseason game. He said nothing publicly about it. Nobody noticed. He did it for the next game. Nobody noticed. After the third game, someone noticed and he was asked why. This was his response:

I am not going to stand up to show pride in a flag for a country that oppresses black people and people of color. To me, this is bigger than football and it would be selfish on my part to look the other way. There are bodies in the street and people getting paid leave and getting away with murder.

At first, I was not thrilled. I always stood during the national anthem with my hand on my heart and facing the flag. I felt I could do that while still acknowledging the failures of my country. I felt these issues should be sorted out in the political and legal systems. However, I definitely supported the right of Colin Kaepernick to freely express his views in peaceful protest. In his situation, I might do the same. After all, I’m white, and I did not grow up in a minority community that suffers a disproportionate amount of arrests, incarcerations, deaths, and longer prison sentences.

Not everybody with the San Francisco 49ers organization was thrilled, but they did recognize his right to peacefully protest by sitting during the national anthem. The team offered this statement:

The national anthem is and always will be a special part of the pre-game ceremony. It is an opportunity to honor our country and reflect on the great liberties we are afforded as its citizens. In respecting such American principles as freedom of religion and freedom of expression, we recognize the right of an individual to choose and participate, or not, in our celebration of the national anthem.

That is a concise statement reflecting knowledge of the US Constitution and a reflection of American values, much more enlightened than the response of some politicians.

Kaepernick began kneeling only after meeting with former Green Beret Nate Boyer, who served tours in both Afghanistan and Iraq. SBNation gives this account:

From the time the protest gained attention, Kaepernick reiterated he was not doing it to be anti-American or anti-military or to disrespect troops. He was doing it to bring serious social issues to light and try to evoke change. That stance led to him slightly adjusting the protest. Kaepernick met with former Green Beret and brief NFL long snapper Nate Boyer, and after the discussion decided to shift from sitting to taking a knee during the anthem.

Several other players joined in during the 2016 season to support bringing attention to racism and racial tension as it exists in the United States.

When Kaepernick announced his free agency and was not picked up, it was conjectured that many NFL teams were reluctant to bring the controversy to their teams. In March of this year, Kaepernick stated that he felt the protest had accomplished it’s purpose and he no longer wanted it to be a distraction, so he would stand during the national anthem in 2017. Whether he did this for his career or not does not matter.

After the white supremacist rally in Charlottesville, VA early this August more NFL players began to kneel during the national anthem to call attention to racism and racial injustice. On August 23, Sports Illustrated published a list of over 50 NFL players, both black and white, that had protested during the national anthem up to that point in the season, along with an entire team.

Not all NFL players supported the protests. They did not welcome the distraction. However, the overwhelming majority felt that players definitely had the right to do so and that they should not be penalized by owners for exercising that right. Many of the NFL owners also supported the right of their players to participate in such a protest.

Then, on Friday, August 23, President Trump, at a campaign rally for Republican candidate Luther Strange in Alabama, said this:

Luther and I, and everyone of us in this arena tonight, are unified by the same Great American values. We’re proud of our country. We respect our flag. Wouldn’t you love to see one of these NFL owners, when somebody disrespects our flag, to say, “Get that son of a bitch off the field right now. Out! He’s fired. He’s fired!”

Only, these protestors had made it clear that their purpose was not to disrespect the flag, but to call attention to racial injustice. By totally ignoring that issue and instead making the protest solely about disrespecting the flag, and then using a line from his reality TV show – “You’re fired!” – President Trump riled up his supporters, who quickly lined up on his side of this fabricated issue. Many of his critics automatically lined up on the other side. The end result is a country that is further divided instead of being focused on solving problems and issues. Lately, this issue has made more news than the failure of the Repeal and Replace bill, the special counsel investigating Russian interference in the election, or statements by the President about totally destroying North Korea, which seems to have emboldened them.

After the President’s statement, the NFL, many more NFL owners, and many more players came out in support of the protests, kneeling or linking arms in solidarity, and have made statements as to why:

• They are protesting the attempt by President Trump to tell NFL owners how to treat their players.
• They are protesting President Trump’s attempt to silence a player for exercising his right to free speech and peaceful protest.
• They are protesting the attempt by President Trump to divide the NFL and the country.

So, that’s how it started, and that’s how it got to where it is now.

As I mentioned, I was not a particular fan of calling attention to racism by kneeling during the national anthem, but I definitely supported the right to do so. To do anything else would be as un-American as it gets. The statement by our President solidified my support. Peaceful protest is often the only way to get people’s attention. It was one of the methods used to get women the right to vote. It was used during the civil rights movement. It was used by US truckers in 1974 when they stopped hauling and drove to Washington DC to protest rising fuel prices and unfair practices by trucking companies. It was used by some police officers when they turned their backs as President Obama was riding by in order to protest his policies. US veterans have dawned their uniforms to assemble in front of the entrance to V.A. facilities to protest the treatment of Veterans.

Also, while some veterans dislike the protest during the national anthem, some are taking knees during the anthem to support the protester’s right to do so.

  And so it goes. I do not care which side of the issue a person is on. You have every right to express your opinion. However, if you want me to listen to your opinion at least make sure you take the time to get your facts straight so you know what the hell you are talking about. Don’t let any politician trick you into lining up on either side of an issue for their own benefit.

Read this extended statement by Colin Kaepernick made in 2016.