As protests by NFL players during the national anthem seem to have settled down, the grievance case against the league by the man who started it all, former San Francisco 49ers quarterback Colin Kaepernick, is proceeding.

You may not have heard much about it lately because it is transpiring behind closed doors. And it is unlike any legal proceeding you might have seen before, not really a trial but with elements of one.

The rules on how the investigation is conducted and by whom — and all the quirks of what evidence is allowed — are detailed in the byzantine labor agreement between the league and players.

It was designed with due process in mind, but as often happens with cases involving the NFL, the decisions often are appealed and end up in federal court.

Kaepernick, who began kneeling last season during the anthem to protest racism and police brutality toward African-Americans, opted out of his contract in March and has not played a down since.

Yet he has become a rallying point for protests, with dozens of players this season at various points kneeling or making some gesture during the anthem, although lately the numbers have trailed off. In the meantime, he has watched about two dozen quarterbacks — including one who came out of retirement — join teams.

Here is a look at his case:

Q. Who will hear the case?

A: Under Article 17 of the labor agreement between the NFL and the players, all cases of collusion are heard by an independent arbitrator appointed by agreement of the NFL and the players’ union. Stephen Burbank, a professor at the University of Pennsylvania Law School, has held that role for many years.

Q. What are the rules for gathering evidence?

A: Unusual for a sports labor agreement, the NFL uses the Federal Rules of Evidence, which are more in line with court trials. This means, among other things, that third-party companies will be hired to help gather evidence, including, for instance, a search of computers and cellphones of league and team officials to find references to Kaepernick. The arbitrator will weigh the evidence and arguments of both sides, perhaps conducting hearings, and make a decision.

Q. What is the definition of collusion in this case?

A: According to the league’s labor agreement, which was last updated in 2011, no team, its employees or agents “shall enter into any agreement, express or implied, with the NFL or any other Club, its employees or agents to restrict or limit individual Club decision-making” negotiations with any player.

Q. How will Kaepernick prove there was collusion to keep him out?

A: Several quarterbacks of seemingly lesser ability or experience have been signed as starters or backups, something Kaepernick’s lawyers point to as evidence teams are deliberately passing over his client.

But proving collusion will be difficult, legal experts say, because teams have many reasons for signing one quarterback over another, including his age, his salary, his temperament, how he fits into an offensive system and other available quarterbacks.

“There’s a host of reasons why a club would individually or independently not offer him a contract,” said Matt Mitten, executive director of the National Sports Law Institute at Marquette University Law School. “So it will be tough for them to argue that there was a tacit agreement.”

Q. How does Kaepernick intend to prove collusion?

A: Kaepernick’s lawyer, Mark Geragos, a prominent criminal attorney based in Los Angeles, has submitted a list of people he wants to depose, including commissioner Roger Goodell and several owners who have been vocal about their opposition to player protests, including Dallas Cowboys owner Jerry Jones and Houston Texans owner Bob McNair.

He will also look for clues in the emails and other documentation from the computer and cellphones searches. The NFL, though, can argue that the document requests are too broad or the requests to depose certain individuals are irrelevant. The arbitrator will ultimately decide on any objections.

Q. Have players won collusion cases in the past?

A: Collusion cases involving individual players are rare in the NFL, but baseball players filed a series of successful cases against Major League Baseball in the 1980s.

Q. What does Kaepernick stand to gain if he wins?

A: According to the labor agreement, Kaepernick would receive twice what he might have earned if he was playing.

Determining what Kaepernick or a quarterback of his caliber might earn is not easy. But according to ESPN, Kaepernick earned at least $12 million (and potentially more in bonuses) last season with the 49ers.

Q. Would the league be forced to give him a shot on a team if it is shown it deliberately kept him out?

A: The league cannot force a team to assess or sign Kaepernick.