Kaepernick unveiled the ad on his personal Twitter, which says, "Believe in something. Even if it means sacrificing everything."
"Pretty powerful when I saw that," said Nike customer Marisa Smith.
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The ad commemorates the 30th anniversary of Nike's "Just Do It" campaign. Kaepernick, who spearheaded a protest movement against social injustice by kneeling during the national anthem, has been out of a job for more than a year, but this latest ad marks a new multi-year deal with the sports apparel giant.
"I think it's more of picking someone who has strong opinions and being independent," said Nike customer Ken Roa.
Nike is already facing criticism. Video of someone burning a pair of Nike shoes appeared on social media. Others question Nike's true motives.
"You've got children in sweatshops making your shoes all over the world, and then you got LeBron putting them on because they say 'equality' so a bunch of people here will buy them. They'll make a bunch of money, but is equality what they're really striving for? Or are they just really trying to sell some sneakers?" asked customer Carlos Rodriguez.
But kinesiology professor Maria Veri of San Francisco State University, an expert on sports culture, believes in the end, the ad campaign will boost Nike's image.
"It's a continuation of a really strong history of athlete activism that Nike is now inserting itself into," said Veri.