Free agent quarterback Colin Kaepernick has been making headlines since recently filing a grievance against NFL owners for collusion.

The controversy began in 2016 when, prior to the start of a game, Kaepernick kneeled during the national anthem in protest of racial inequality in the United States. His refusal to stand during the anthem has now catapulted Kaepernick into a world of unemployment and lawsuits.

In filing a grievance on on Oct. 15, the former San Francisco 49ers quarterback accused NFL teams of conspiring to keep him out of the league.

“Principled and peaceful political protest … should not be punished and athletes should not be denied employment based on partisan political provocation by the Executive Branch of our government…Protecting all athletes from such collusive conduct is what compelled Mr. Kaepernick to file his grievance,” Kaepernick’s attorney, Mark J Geragos said in a recent statement.

The Collective Bargaining Agreement (CBA) prohibits teams from conspiring about players. However, the CBA also says that evidence of collusion must go far beyond the mere fact that a player is unsigned and potentially qualified to play in the NFL. As a result, legal experts speculate how successful Kaepernick will actually be in proving his case.

Any such evidence of collusion by NFL teams against Kaepernick has yet to surface. In order to win the case, Kaepernick and his legal team must present clear evidence that two or more teams conspired against him. They need concrete and convincing proof, as proving collusion in the case of a single player is significantly more difficult than in the case of a series of players.

“There has to be some evidence of an explicit or implied agreement. There has to be proof of a conspiracy,” Gabriel Feldman, director of the Sports Law Program at Tulane University said.

Whether or not they obtain such evidence remains unknown, but all sides considered, Kaepernick did have good reason to believe another team would sign him. In 2016, Kaepernick made $14.3 million as quarterback for the San Francisco 49ers. He held a respectable record of 16 touchdowns and only four interceptions during last year’s season.

It’s also possible, however, that teams independently decided that Kaepernick is too controversial to sign. In this case, collusion will be nearly impossible to determine.