Kaepernick caused a stir when he sat on the bench while the anthem played before an NFL game in August 2016. Asked why he wasn't standing, he said he was sitting in protest over police killings of unarmed black men. He went on to consistently kneel during the anthem, and while he went unsigned last season, a handful of other players had continued the practice.
The new Nike campaign, released Monday night, showed an image of Kaepernick with the words "Believe in something. Even if it means sacrificing everything."
The practice of kneeling during the anthem proved divisive last year, however, with Trump characterizing it as disrespectful to the US flag and military. And on Monday, videos quickly emerged of people burning Nike shoes, cutting Nike's swoosh logo off socks, and in some cases vowing to never buy Nike products again.
Many posts included the hashtag #JustBurnIt, a play on Nike's "Just Do It" slogan.
The country musician John Rich tweeted that his sound technician, whom he described as a Marine veteran, had cut off Nike's signature swoosh from his socks in protest.
The Twitter user ArtenenAeolus shared a video, since deleted, of a man burning some Nike products.
A Twitter user named Kolten Conrad seemed to decide to throw his Nike kit in the trash instead:
The below video appeared on Facebook, with a man saying "I just did it."
Another person posted a video of a Nike shoe-burning on Facebook. "Never again will I wear another Nike shoe," a man's voice can be heard saying.
It's unclear what impact the protests will have on Nike, which earned $34.5 billion (R520 billion) in revenue in its most recent fiscal year.
"Nike ran the numbers. They'll be ok," the actor Zach Braff tweeted.
He added sarcastically: "But please, burn your socks."
The Bloomberg analyst Chen Grazutis also said on Tuesday: "The long-term relationship and a contract that benefits both parties over the next 10 years will likely outweigh any current controversy."
Kaepernick's protests have garnered him support as well as criticism around the world.
Dozens of athletes in football and basketball, as well as cheerleaders and band members, have knelt or sat in protest during the playing of the national anthem.
Trump has slammed athletes who followed Kaepernick's lead.
He suggested last September that NFL owners should stop those who kneel during the national anthem from playing in games. "Wouldn't you want to see one of those NFL owners, when someone disrespects our flag, to say, 'Get that son of a b---- off the field right now'?" he said at a rally.
He also tweeted: "The issue of kneeling has nothing to do with race. It is about respect for our Country, Flag and National Anthem. NFL must respect this!"
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