After an initial backlash and a flurry of bad press, it appears that San Francisco 49ers quarterback Colin Kaepernick's symbolic protest during "The Star-Spangled Banner" is really catching on.

Kaepernick has been deliberately not standing at NFL games during the national anthem of the United States because of the history of racial oppression in the country, and more specifically the recent spate of unarmed black men killed under suspicious circumstances.

During the NFL's first weekend of regular season games—and ironically on the 15th anniversary of the terrorist attacks of September 11, 2001—a number of players demonstrated solidarity with the 49ers star through silent demonstrations while the song was played:

Patriots Martellus Bennett & Devin McCourty raise clenched fists at end of “The Star-Spangled Banner’’ Sunday night. pic.twitter.com/nNPTdQt9ts — John Nichols (@NicholsUprising) September 12, 2016

The Chiefs’ Marcus Peters raised his fist during the national anthem ahead of a NFL game https://t.co/zkMvqjLRgO pic.twitter.com/6lznHhdpOy — The New York Times (@nytimes) September 11, 2016

After days of speculation that the entire Seattle Seahawks squad would sit out the national anthem, all 53 members of the team and their coach Pete Carroll linked arms in a display of unity during the song.

There you go. After all the speculation. Seahawks players & coaches all linked arms in unity during anthem #MIAvsSEA pic.twitter.com/LgfROF5kdB — Greg Thies | KING5 (@K5Greg) September 11, 2016

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To express a desire to bring people together, our team will honor the country and flag in a pregame demonstration of unity. — Doug Baldwin Jr (@DougBaldwinJr) September 8, 2016

"I spoke with the players, and they realize that 9/11 is a very important day in our nation's history. The Seahawks, and probably every team, will be honoring those who serve in camouflage and also those in blue who served on such a difficult day," Nate Boyer, a former Green Beret who had a short stint with the Seahawks as an undrafted free agent last season, told Fox Sports Radio.

"Shortly after 9/11, our country seemed more unified than I had ever experienced and was the most unified it has been since I have been alive. Since that date, we have grown farther apart in our unity," Boyer said. "Standing together this Sunday is key to making progress. What the team will do is a powerful sign of unification."

Inside the conversation between Colin Kaepernick and Army hero Nate Boyer



This is powerful.https://t.co/RLnYmllkp3 pic.twitter.com/bySyXKGb6I — Sporting News (@sportingnews) September 2, 2016

"It has to be a team-first approach in order to get anything done," he added. "Whether it is Kaepernick's mission-changing policy or changing things on the field, you have to be unified."

Even though the Seahawks' demonstration has received widespread praise, not everyone was pleased with the increasing outspokenness of NFL stars.

“Dear @NFL Any player wants to boycott the anthem on 9/11 should be asked to remain in the locker room until kick off. It’s not their moment,” wrote actor Rob Lowe on Twitter.

Supermodel Kate Upton went even further, calling NFL player protests on the 9/11 anniversary "horrific" in a lengthy Instagram post. “Sitting or kneeling down during the national anthem is a disgrace to those people who have served and currently serve our country,” Upton wrote.

"Protest all you want and use social media all you want. However, during the nearly two minutes when that song is playing, I believe everyone should put their hands on their heart and be proud of our country for we are all truly blessed,” she added, before citing the election of Barack Obama as the first African-American U.S. president as proof that the country has turned a corner on race.

After receiving considerable pushback on social media, Upton conceded that the justice system is "corrupt."

Maybe you can be proud to be an American and also protest those things that you think aren't so great about America. https://t.co/klwSIB4DNR — Soledad O'Brien (@soledadobrien) September 11, 2016

Meanwhile, Republican presidential nominee Donald Trump, who is infamous for weighing in on sports matters, made his displeasure with the weekend's activities known during a "Fox and Friends" call-in appearance early on Monday.

"I think it's a lack of respect for our country. I think it's a lack of appreciation for our country and it's a very sad thing. I've never seen anything quite like it actually," Trump said.

Related: Colin Kaepernick's Protest is Part of Long Sports Tradition

Trump went on to repeat his past suggestion that Kaepernick and like-minded football stars "should try another country, see if they like it better."

"See if they'll make 20 million dollars a year for being the second string quarterback," the Republican presidential nominee added in a direct dig at Kaepernick's diminished status on the football field.

As for the official franchises and the league itself, the leadership of the NFL has walked a much more egalitarian line when it comes to the political protests of players.

For instance, in an official statement, the Miami Dolphins said that while they encourage members of their organization to stand during the anthem, they also "recognize that it's an individual's right to reflect during the anthem in different ways."

NFL Commissioner Roger Goodell, no stranger to controversy himself, has said that while he doesn't necessarily support the statements and protests of Kaepernick and company personally, he is pleased that the league has been able to accommodate their freedom of speech.

"We play a role in society, an important role in society. We understand that," Goodell told NBC's Matt Lauer last week prior to the games on Sunday. "We're careful about that because we still believe that at the bottom people come to enjoy the sport, they come to enjoy the game. But they recognize the importance that the NFL plays in our society. And we all have to be responsible for that."

"We encourage our players to be respectful," Goodell added. "But they also have rights and we have to respect that."

However, outside the NFL, athletes may not enjoy the same protections that professionals enjoy. Rodney Axson, a 16-year-old high school football player from Ohio, has reportedly been subjected to racial slurs and threats because he chose to take a knee during the anthem as an homage to Kaepernick.