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Nike dropped 2.9% in trading Tuesday after the sneaker giant revealed Colin Kaepernick as the 30th anniversary face of its famous "Just Do It" ad campaign.

The former San Francisco 49ers quarterback — and leader of polarizing protests during the national anthem — has not played since 2016, when he opted out of his contract with the San Francisco 49ers.

He has since accused team owners of collusion to keep him out of the league. An arbitrator ruled last week that his case against the NFL can proceed to a full hearing, despite objections from the league.

"Believe in something, even if it means sacrificing everything," the 30-year-old said in a tweet Monday that included a photo from the campaign. Nike has represented Kaepernick since 2011, but hasn't featured him in ads for two years, according to ESPN.

Colin Kaepernick via Twitter

The issue of players kneeling during the National Anthem could once again take center stage as the NFL season kicks off on Thursday. The players' union and league officials remain deadlocked over a May agreement between the two groups which said players would not be required to be on the field for the anthem, but any player who was on the field must stand or face a fine.

"Nike supports athletes and their right to freedom of expression on issues that are of great importance to our society," the company said in a statement last year when it faced backlash for supporting Kaepernick amid his protests against racial injustice and police brutality.

Nike is used to making a splash

When the French Open banned Serena Williams' black catsuit in August, the company released an image defending her that said, "You can take the superhero out of her costume, but you can never take away her superpowers."

The original "Just Do It" ad campaign premiered in 1988, when Nike featured 80-year-old Walt Stack jogging across the Golden Gate Bridge. Kaepernick's spot is in celebration of the ad's 30th anniversary, ESPN reported.

"We believe Colin is one of the most inspirational athletes of this generation, who has leveraged the power of sport to help move the world forward," Nike's vice president of brand for North America Gino Fisanotti told ESPN.

Nike shares are up 29.5% this year, but boycotts could hurt the brand — at least if the vitriol from Twitter hurts sales. The hashtag #NikeBoycott was among the top trending topics on Twitter on Tuesday morning, with users posting images of themselves burning and ripping their Nike shoes and apparel, Reuters reported.

For now, though, it's not clear how much of Tuesdays' decline was actually related to the backlash. Other sneaker companies including Adidas were down similar measures thanks ongoing trade war negotiations between the White House and other countries.

Rebecca Harrington contributed to this article.

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