The NFL's concussion protocol, authored and administered jointly with the NFL Players Association, has come under fire in 2017. The most recent criticism came this week, when Houston Texans quarterback Tom Savage returned to Sunday's game against the San Francisco 49ers after suffering a hit to the head so severe that he displayed apparent signs of what's known as the "fencing response," a classic indication of a brain injury that includes twitching hands.

Known formally as the "Game Day Concussion Diagnosis and Management Protocol," the policy in theory should prevent such health-threatening returns to play. That hasn't always been the case this season, as Savage is one of a handful of players who have remained in a game after a hit that was later identified to have caused a concussion.

Here's how the protocol is supposed to work:

Wait ... can we further clarify 'fencing response'?

Yes. Sometimes a concussion can induce the victim's arms to lock in an odd position, similar to a competing fencer: one arm at the side and the other extended outward. In Savage's case, both arms were extended. Regardless, it is considered a clear indication of brain trauma.

OK, thanks. So let's start from the beginning. How does the policy work on game day?

It begins with the positioning of four independent and dedicated medical professionals. Two certified athletic trainers (ATCs) sit in a booth above field level, acting as "spotters" equipped with video playback gear and a dedicated radio connection with the sidelines. Each team is also assigned an unaffiliated neurological consultant (UNC), who works alongside the team doctor.

'Unaffiliated'?

Yes. The point is to include a medical specialist who doesn't have a stake in the outcome of the game.

Does the NFL have video equipment on the sideline as well?

Yes. Because sideline views can be blocked, each UNC has access to video replays. According to the policy, they can "review the game film on the sidelines to obtain information on particular plays involving possible injury." This equipment is reserved for the medical staff, because football employees are barred from seeing replays on the sideline.

Who is responsible for initiating the process?

Players are encouraged to self-report, and the team doctor has ultimate responsibility for care. But the ATC spotters in the booth have the authority to call a medical timeout if they identify a player with symptoms. The referee also is asked to send players to the sideline if they see a player displaying symptoms.

How do they identify players for concussion testing?

Aside from the obvious -- loss of consciousness, amnesia or confusion -- medical staffs are trained to look for a "blank or vacant" look, a slow rise from the ground, balance issues, or a clutching of the head after contact. In addition, players are to be tested if they report a headache, dizziness, balance difficulties, nausea, amnesia, disorientation, a ringing in the ears or sensitivity to light or sound.

What takes place during the initial test?

Players are taken to the blue medical evaluation tent for what's known as a "sideline survey." The test is expected to include questions about the history of the event, which players often don't remember if they are concussed. The team doctor and UNC use "Maddock's questions" -- a standard part of sports concussion tests that, for example, could include asking a player to recite months in reverse order or to complete a word recall exercise. The policy also calls for video review of the hit, a place where the treatment of Savage might have broken down, and a focused neurological exam that includes a cervical spine examination, evaluation of speech and observations of gait as well as eye movement.

Then what?

If any elements of the sideline survey lead to a "positive, inconclusive or suspicious" assessment, according to the policy, the player must be taken to the locker room for what's known as a complete "NFL Locker Room Comprehensive Concussion Assessment." If not, they are cleared to return to the game.

And that's it for the cleared players?

No. The policy suggests a best practice of periodically checking back with the player after the original examination. That player must be sent to the locker room if symptoms appear or worsen. Many concussions can have delayed onset.

Who is responsible for making these decisions?

The policy states that the team doctor is responsible for all decisions but must consult with the UNC before finalizing. According to the policy: "If the UNC disagrees with the team physician’s decision to return the player to play or remove the athlete, the UNC will be given an opportunity to explain the basis of his/her opinion. This will be discussed in a collegial fashion in private as to why that the player should or should not be returned to the game. The team physician will communicate his final decision to the player."

What happens in the locker room?

The NFL uses the "SCAT 5," a standard concussion assessment tool published by the International Concussion in Sport Group. In essence, it is a more comprehensive version of the sideline test. When available, its results are compared to the "baseline" tests players take when they are healthy in the preseason. A score lower than the baseline indicates a concussion.

Is that score the deciding factor?

No. The policy allows the team doctors to rule out a player and begin treatment, even if the scores are essentially equal, based on the doctor's knowledge of the player.

What is the treatment?

Players in the NFL concussion protocol must move through a five-step process that can't end until both the team doctor and an independent neurological consultant clear him for return to participation. There is no minimum or maximum for time spent in the protocol, and players can be cleared to participate in some parts of practice before getting the go-ahead to play in a game. The five steps include:

1. Rest and recovery

2. Light aerobic exercise

3. Continued aerobic exercise/strength training

4. Football specific activities

5. Full football activity/clearance

Do the NFL and NFLPA have a way to enforce this policy?

Yes. Prior to the 2016 season, they established a series of club disciplines for failure to comply. A first violation requires remedial education for medical officials and/or a maximum $150,000 fine. A second violation calls for a minimum $100,000 fine. Ultimately, if the NFL determines that the club's medical staff violated the policy for competitive reasons, additional fines and a potential forfeiture of draft picks can occur.

Anything else?

That about covers it. One final point to make is that all of these rules and regulations appear reasonable and clear on paper, but can get jumbled and harried during live game action. That's not to excuse a failure to comply, but it might explain why it happens sometimes.