WHEN Jacob Hopper dived to smother a kick from Port Adelaide's Karl Amon in round 20, he arrived too late to get a hand on the ball and ended up in the path of a swinging left boot that hit him in the face.

As Hopper collapsed to the ground, Greater Western Sydney's medical team rushed onto the field and were beside the midfielder within a few seconds.

A concussion assessment wasn't a priority at this stage, as Hopper's symptoms were obvious, but that test would become an important and regular part of his clearance for playing 12 days later against Richmond.

Bassam Moses, chief medical officer at GWS, takes AFL.com.au inside those tense moments on the field, what happens after a player is removed from the play, and the steps a concussed player works through as part of the return to play protocols.

"With Jacob Hopper's incident, or any incident where the player is semi-unconscious or unconscious, the main priority is to get to the player as quickly as we can, check their breathing, then check their neck," Moses said.

"The collar will go on to support the neck and spine, and they'll go off on the stretcher. A lot of the time that's precautionary but you need to make sure the player is lucid before you assess their neck properly and clear them of a spinal injury."

Once the doctor is sure the player hasn't injured their neck or spine, they will check for facial and eye injuries and only then assess them for concussion.

Reviewing the replay

Incidents that lead to concussion aren't always as obvious as the one involving Hopper against the Power. Earlier in that same match, his teammate Phil Davis was subbed out with what was initially thought to be a neck injury.

Davis was hurt when he went to pick up the ball as Todd Marshall kicked it off the ground, and the Power ruckman's hip hit Davis on the back of the head and neck. The Giants defender didn't show immediate concussion symptoms but the medical team turned to replays to review the incident.

"The vision is very important and helpful. There is a list of criteria that we're looking for on the vision to help us make either a diagnosis of concussion or at least that the player needs to come off and be assessed," Moses said.

"It's mostly not about the contact or the injury, it's what happens afterwards."

The 'Category A' criteria points to a player being concussed and includes:

• loss of consciousness
• no protective action like using hands to break the fall
• a seizure or the hands become rigid (known as 'tonic posturing')
• loss of coordination or balance
• a dazed, blank or vacant stare
• confusion, disorientation or the player just isn't themselves (e.g. the player runs to a part of the field that is inappropriate or unusual for them)

The 'Category B' criteria shows that a player needs to be brought from the field and assessed, and includes lying motionless for more than two seconds or 'possibly' experiencing any of the Category A criteria.

There are also additional doctors, known as 'spotters', watching on screens to look for incidents of concern. The spotters will contact AFL officials at the ground or the club doctors directly if they think a player might need to be taken off the ground and assessed.

How a concussed player is assessed

The concussion assessment includes a symptoms checklist, questions to test memory and comprehension, and four balance tests.

Each player goes through the same assessment in the pre-season, so the medical team has a baseline to compare them to if needed during the season.

The checklist considers 26 symptoms like having a headache, dizziness, nausea, vomiting, and feeling 'slow', emotional or irritable.

"The player rates their symptoms based on 0 being nothing to 6 being the worst they've experienced in their life," Moses said.

The next test is on memory recall and might include asking the player where they are, what quarter it is, who they played last week and whether they won or lost.

Further tests can include giving the player 10 words to remember and repeat three times, giving a series of numbers to say in reverse, or asking them to say the months of the year backwards.

The players then go through these balance tests:

• Walk heel-to-toe for 3m, turn around and come back
• Stand with feet together side-by-side, hands on hips and eyes closed for 20 seconds
• Stand on the non-dominant foot, hands on hips and eyes closed for 20 seconds, lift the dominant foot off the ground
• Stand with the non-dominant foot behind the dominant foot heel-to-toe, hands on hips and eyes closed for 20 seconds

"We compare it all to their baseline and see if they're way off how they normally perform, or are pretty much where they usually are. It's there to guide us in our decision-making," Moses said. 

"If you're uncertain, you say the player has a concussion until proven otherwise. The player's safety is the priority."

Getting back on the field 

The earliest a concussed player can return to play is on the 12th day after the match or incident, and they must complete all phases in the recovery process and receive a medical clearance.

If a player experiences further symptoms at any stage they will repeat that step the next day until they can complete it without any problems.

These are the return-to-play protocols that concussed players like Hopper and Davis have to progress through:

Day after match/incident: Rest day. Avoid activities that require a lot of concentration until all symptoms have cleared. Symptoms usually clear within 24 hours of the match or incident, but this is the most likely period for recovery to be delayed.

Day 2: Normal daily activities.

Day 3: Very light aerobic exercise. Start of the 'individual program' away from the team. This is the step where symptoms are most likely to return and recovery delayed, especially where the player tries to progress too quickly.

Day 4: Light aerobic exercise. This might mean a walk, jog or slow bike ride.

Day 5: Light activities to increase the heart rate. This might include stationary kicking or handballing drills, or light resistance training in the gym.

Day 6: Non-contact training session. Start of the 'graded loading program' with the team but the player must be pulled out of any drills that include contact or are likely to cause contact. 

Day 7: Rest day. Can do a weights session.

Day 8: Limited contact training. Can do drills where there might be incidental contact but must not join in full contact drills.

Day 9: Rest day. Can do a weights session. The player will also complete a computer-based test on speed, accuracy and memory recall that is compared to a pre-season baseline.

Day 10: Full contact training. This must be done with the team as normal in the main training session and include contact-like bumps and tackles. The Giants had to have their main session on Wednesday this week to allow Hopper and Davis to progress through the protocols in time to possibly return to play on Friday. 

Day 11: Rest day. Can include the captain's run.

Day 12: Final assessment. If cleared, the player can return to play.

Hopper and Davis were both cleared to face Richmond on Friday night, but only Hopper was selected with the Giants sticking with the same back seven that performed brilliantly against Geelong last week.

"The feeling of not being yourself and not being able to explain what it is, is one of the worst experiences," Davis said on the Giants' weekly podcast The Footy Phil a few days after the match against the Power.

"You feel like you're letting the team down because physically you're capable. But I will never apologise for putting my brain ahead of football and I'll do that for the rest of my career."