Concussion in Sport: What the Protocols Get Right, and What CTE Research Still Cannot Prove

A concussion is an invisible injury. There is no swelling to point at, no scan that reliably shows it, and an athlete can insist they feel fine while their brain is still recovering. That combination, an injury you cannot see and a competitor who wants to keep playing, is exactly why sport has spent two decades building protocols to take the decision out of the heat of the moment. Those protocols have improved a great deal. The harder question, whether repeated head impacts cause long-term brain disease, has a clearer answer than it did ten years ago but still carries real uncertainty.

What a concussion actually is

A concussion is a mild traumatic brain injury caused by a blow to the head or body that transmits force to the brain. It disturbs brain function temporarily, producing symptoms such as headache, confusion, dizziness, sensitivity to light and trouble concentrating. Crucially, most concussions do not involve loss of consciousness, which is one of the most persistent myths in sport. An athlete who never blacked out can still be concussed.

The danger is not usually a single concussion, most of which resolve within a couple of weeks. The danger is a second impact before the first has healed, and the cumulative effect of repeated knocks over a career.

Sideline tools: HIA and SCAT

The frontline of concussion management is the sideline assessment. The Sport Concussion Assessment Tool, now in its sixth edition as SCAT6, is a standardized battery checking symptoms, memory, balance and cognition. It is built on the international consensus statements coordinated through the Concussion in Sport Group, published in the British Journal of Sports Medicine.

In contact sports, a Head Injury Assessment, or HIA, lets medical staff remove a player and evaluate them off the field. World Rugby’s HIA process is among the most developed, with a temporary substitution allowing a proper off-pitch assessment rather than a rushed pitchside guess. The tools are not perfect, because no single test diagnoses concussion definitively, but they impose structure and, importantly, remove the player from the immediate decision. The guiding principle across codes is blunt and sound: if in doubt, sit them out.

Graduated return to play

Once diagnosed, an athlete follows a stepwise return-to-play protocol rather than jumping straight back. The standard framework moves through stages: symptom-limited rest, then light aerobic exercise, sport-specific drills, non-contact training, full-contact practice and finally competition. The athlete must remain symptom-free to advance, and any return of symptoms means dropping back a stage.

This staged approach exists for a sober reason. Returning while still symptomatic risks second-impact syndrome, a rare but catastrophic swelling of the brain, and prolongs recovery. Recovery and load management here share principles with broader recovery science, where the temptation to rush back is the recurring enemy.

CTE: real, but not as simple as headlines suggest

Chronic traumatic encephalopathy, or CTE, is a neurodegenerative disease found in the brains of some people with a history of repeated head impacts. It is defined by a specific pattern of an abnormal protein, tau, accumulating around small blood vessels deep in the brain. The leading research center is the Boston University CTE Center, which has examined hundreds of donated brains, including a widely reported series in which CTE was identified in a very high proportion of former American football players.

Three things are established. CTE is a genuine disease with a distinct pathology. It has been found in athletes from football, boxing, rugby, hockey and other contact sports. And the strongest known risk factor is the cumulative burden of repetitive head impacts, not just diagnosed concussions, which means the sub-concussive hits that never get flagged may matter most.

Three things are not yet settled, and honesty requires stating them. First, CTE can currently only be diagnosed for certain after death, so the living prevalence is unknown. Second, the brain banks that produced the alarming percentages are not random samples, because families donate brains precisely when they suspect a problem, which inflates the apparent rate. Third, the relationship between the pathology seen under a microscope and the symptoms a person experienced in life, including mood changes and dementia, is still being worked out. CTE is real and worth taking seriously. It is not yet something we can measure in a living athlete or predict for an individual.

How the major sports have responded

The governing bodies have moved at different speeds. The NFL, after years of resistance, now operates a detailed concussion protocol with independent neurotrauma consultants on the sideline and spotters empowered to stop play. World Rugby has pushed graduated return-to-play, the HIA process and law changes lowering the legal tackle height to reduce head contact. Football’s governing bodies, including FIFA, have faced criticism for being slower, though concussion substitutes and stricter assessment have been trialed and expanded.

The broader trend is prevention by reducing exposure: limiting full-contact training, changing rules, and in some youth settings delaying heading or tackling. The wearable sensors that measure head-impact loads, part of the wider move toward data in elite sport, may eventually help quantify the cumulative burden that CTE research points to.

FAQ

Does every concussion lead to CTE? No. Most concussions resolve fully within days to weeks with proper rest and graduated return. CTE is associated with the cumulative burden of repeated head impacts over a long period, and even among athletes with heavy exposure, not all develop it. The exact dose-response relationship is not yet known.

Can CTE be diagnosed in a living athlete? Not reliably. At present a definitive CTE diagnosis requires examining brain tissue after death. Researchers are developing imaging and biomarker methods to detect it in life, but none is yet validated for routine clinical use, which is why claims about a living person “having CTE” should be treated cautiously.

Is it safe to return to play once symptoms go away? Symptom resolution is necessary but not sufficient on its own. Athletes should complete a graduated, stepwise return protocol, staying symptom-free at each stage before advancing. Returning to contact too soon, especially before full recovery, raises the risk of prolonged symptoms and, rarely, severe second-impact injury.

Sources

1. Consensus statement on concussion in sport, Amsterdam 2022, British Journal of Sports Medicine
2. Boston University CTE Center
3. Head Injury Assessment and concussion management, World Rugby
4. NFL Head, Neck and Spine Committee concussion protocol, NFL Player Health and Safety
5. Sport Concussion Assessment Tool 6 (SCAT6)
6. Chronic traumatic encephalopathy overview, Concussion Legacy Foundation