When Nike announced on Monday that Colin Kaepernick would be part of a major advertising campaign, some people cheered. Others burned their shoes and ripped their socks.

Kaepernick, a former quarterback for the San Francisco 49ers who is now a free agent and pursuing a collusion case against the NFL, rose to political prominence in 2016 after he began kneeling during the playing of the national anthem at his games to protest racial inequality and police killings of black people. Critics have accused him of disrespecting the anthem and, by extension, the military and the American flag.

Now Kaepernick will be a face of the 30th anniversary of Nike’s “Just Do It” campaign. In the wave of reaction that immediately followed that announcement, one tweet by a member of the country duo Big & Rich captured the sentiment of those who opposed the decision. John Rich, a part of the duo, shared a photo of socks with the Nike swoosh cut off.

“Our Soundman just cut the Nike swoosh off his socks,” Rich wrote. “Former marine. Get ready @Nike multiply that by the millions.”

By this afternoon, that tweet had been shared more than 11,000 times. Others shared photographs and videos of Nike shoes that appeared to be on fire or in the trash.

Andrew Morse, who lives near Detroit, saw Rich’s photo and recalled thinking, “What a weird thing to do.”

“If you don’t want to wear them, you can do something with those socks,” Morse said in an interview today. “Someone could be using those socks right now.”

After seeing Rich’s tweet, Morse bought 30 pairs of Nike socks on Amazon and sent them to Alternatives for Girls, a Detroit nonprofit that helps at-risk women and girls. He shared a photo of his purchase on Twitter.

Before Monday, Morse, who owns an HVAC company and runs a Detroit Lions fan page on Twitter and YouTube, said he had not previously favored Nike apparel over other sports brands. But that changed after Nike unveiled the campaign and he saw the opposition to it online, he said.

“It makes me proud of Nike in a way that they would stand for what they believe in,” Morse, 31, said.

Many people voiced similar sentiments online, pledging to buy Nike products or showing their receipts. Nike was also commended by some athletes, including Eric Reid, who was one of the first NFL players to protest with Kaepernick and is now himself a free agent pursuing a grievance against the league, as well as Serena Williams, who signed onto the new ad campaign alongside Kaepernick.

Even the former CIA director John O. Brennan weighed in with support, writing on Twitter that Kaepernick “drew our collective attention to the problem of continued racial injustice in America.”

But critics of the decision pledged to boycott Nike products, and a #BoycottNike hashtag spread on Twitter. (It was unclear how widespread or organized such a boycott might be.)

Many shared a version of the Nike ad altered to show the face of Pat Tillman, who left the Arizona Cardinals to join the Army and was serving in Afghanistan when he was killed in 2004. (His widow has asked that his memory not be politicized.)

And some, including former Fox News anchor Bill O’Reilly, criticized Kaepernick’s stance toward the police, pointing out that the player had worn socks depicting cartoon pigs in police caps.

When Kaepernick began kneeling in 2016, he inspired a wave of similar protests, both on and off the fields of the NFL. The issue became as high profile as it was polarizing; President Donald Trump has used expletives to criticize kneeling players and has called for them to be fired.

Kaepernick accused the NFL of colluding to keep him off the field because of his activism, and he scored a victory when an arbitrator let his case advance in a ruling disclosed last week.

In a statement today, Jocelyn Moore, a spokeswoman for the league, said, “The social justice issues that Colin and other professional athletes have raised deserve our attention and action.”

Some people reacted to the Nike campaign with mixed feelings, noting that the company’s decision was likely to be good for business.

Nike’s stock price fell more than 2 percent in early trading today. While some investors were most likely nervous that the Kaepernick announcement would inspire boycotts, the stock price of a main competitor, Adidas, was also down more than 2 percent amid a broader downturn, which was partly attributed to worries about tense negotiations over NAFTA.

Rosa Clemente, an activist and political commentator, said she supported Kaepernick but was disappointed to see him teaming up with the corporation.

“Activists, organizers and leaders sometimes make mistakes, and I think he made a mistake by aligning himself with a company that exploits workers and breaks unions,” Clemente, 46, said in an interview today. “It’s not just a capitalist company — it’s a hypercapitalist company.”

David M. Carter, the executive director of the Sports Business Institute at the University of Southern California, Marshall, said Nike had tried to brand itself as a company that supports individual athletes and could benefit from keeping Kaepernick’s activism in the news cycle.

“I think it’s very consistent with the Nike brand, and I think what is different about what we’re seeing today is that this is happening in this era of immediacy, with the media and the keyboard warriors out there on both sides, making their point,” Carter said in an interview today.

Nike was criticized in the 1990s over reports that employees at overseas factories were working long hours for low pay and in dangerous conditions. In 1998, the company pledged to root out illegal labor practices, but criticism and protests have continued.

The company says that it “does not own or operate the facilities which produce our products,” adding, “However, we are prioritizing and growing relationships with suppliers who share our commitment to respect human rights and are investing in their workforces.”

This year, Nike also reckoned with the #MeToo movement when women at the company’s headquarters in Beaverton, Oregon, came forward with complaints about marginalization and a toxic work environment, which led to the departures of several high-level executives.

Clemente said that it was “fascinating” to see opponents of Kaepernick taking a stand against a large corporation like Nike. “They are taking from our playbook of protest,” she said.

© 2018 The New York Times Company