Ask Farmer: How exactly does the NFL’s concussion protocol work?

Have a question about the NFL? Ask Times NFL writer Sam Farmer, and he will answer as many as he can online and in the Sunday editions of the newspaper throughout the season. Email questions to: sam.farmer@latimes.com

Could you please explain how a concussion is determined during an NFL game, and what the protocol entails for return to play. Some players are on the injured list for a week, some longer. Who makes the decision to return?

Pat Hansen, Downey

For the last several years, the NFL has been refining the way it handles players who have sustained head and neck injuries, including concussions.

First, the system depends on someone recognizing that the player in question needs to be evaluated. It might be a team doctor or trainer who sees that. Maybe it’s a coach, a teammate, an official, or the independent spotter who is watching from the press box and now has the authority to stop the game.

Once the player in distress is identified, he is evaluated on the sideline by a team doctor and an unaffiliated neuro-trauma consultant (a concussion specialist paid by the league).

If there are any signs of a concussion, the player is taken to the locker room, and the team doctor and unaffiliated doctor perform a more comprehensive examination.

The two doctors consult and make a diagnosis. If a player has sustained a concussion, he cannot return to play.

Then comes the concussion protocol: During the course of his recovery, the player goes through a series of stages — such as asymptomatic at rest, moderate exercise — that are normally overseen at the team’s facility by the team medical staff.

When all the stages are completed, it’s up to an independent doctor jointly appointed by the NFL and NFL Players Assn. to clear him to play, regardless of the amount of time it takes.

If the starting quarterback comes out of a game for any reason, can he return later in that same game?

Rick Immel, Chatsworth

The short answer is, yes, the starting quarterback is allowed to return, except if he has been diagnosed with a concussion.

But the rules didn’t always allow for that. In 2011, the NFL expanded the active roster from 45 to 46 and got rid of the emergency third-quarterback designation.

Before that, a team could switch out its starter and backup at any time in a game, back and forth at your its pleasure. But if it used its No. 3 quarterback at all before the fourth quarter, a team could not go back to quarterbacks Nos. 1 or 2 quarterbacks.

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