Colin Kaepernick (R), and Eric Reid of the San Francisco 49ers (L), kneel in protest during the national anthem prior to playing the Los Angeles Rams at Levi's Stadium on Sept. 12, 2016 in Santa Clara, California.
Colin Kaepernick (R), and Eric Reid of the San Francisco 49ers (L), kneel in protest during the national anthem prior to playing the Los Angeles Rams at Levi's Stadium on Sept. 12, 2016 in Santa Clara, California. - 
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Colin Kaepernick — the football player who started kneeling during the national anthem to protest social injustice — has now filed a grievance against the NFL, accusing its teams of colluding against him.

He opted out of his contract with the San Francisco 49ers in March, and no team has signed him despite a strong season last year. That's led to speculation in the sports community that he’s been blackballed by the NFL because of his political activism.

In August of last year, Kaepernick said he refused to stand for the national anthem because of racial inequality that exists in the U.S. 

"I am not going to stand up to show pride in a flag for a country that oppresses black people and people of color," Kaepernick said. "To me, this is bigger than football and it would be selfish on my part to look the other way. There are bodies in the street and people getting paid leave and getting away with murder."

Back in September, hundreds of football players, coaches and NFL owners engaged in their own forms of protest (which included kneeling) after Donald Trump called on NFL owners to fire football players who do not stand during the pledge of allegiance.

The NFL is bound by a collective bargaining agreement, which mandates that Kaepernick's case be handled through arbitration. It'll be up to Kaepernick show evidence of collusion and prove that the teams actively conspired against him. It’s not enough to point out that he’s a talented player and hasn’t been signed — the collective bargaining agreement actually says that explicitly. Kaepernick and his team have to meet a higher level of proof. 

Kaepernick’s hired Mark Geragos, a high-profile lawyer who said in a tweet that they filed a grievance after exhausting all other options with the teams. 

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