Concussion cannot be confirmed by imaging in the way a fracture can. Assessment depends instead on detecting a change from how a specific athlete normally performs on a set of tasks.
The injury is functional rather than structural
A concussion disturbs how brain cells signal and how they manage energy. Standard scans look for bleeding or structural damage, which in most concussions is absent.
A normal scan therefore does not exclude the injury. Scans are ordered to rule out more serious problems, not to answer whether a concussion occurred.
What remains measurable is function: reaction time, memory, balance, eye movement control and reported symptoms. All of these vary widely between healthy people.
Population norms are too broad to be useful
An athlete who scores below average on a memory task may always have scored there. Without knowing their usual result, a below-average score after a collision carries little information.
The reverse is more dangerous. Someone whose normal performance is well above average can suffer a substantial decline and still land inside the population's normal range.
Baseline testing resolves this by making each athlete their own comparison. The question becomes how far they have moved from their own result, which is far more sensitive.
Baselines have to be collected honestly
The system fails if athletes deliberately underperform at baseline to make a later comparison look normal. This is a recognised problem wherever selection or availability is at stake.
Testing protocols address it by supervising sessions, repeating tests, and flagging results that look implausibly poor for a healthy competitor.
Baselines also drift. Cognitive performance changes with age and development, which is why testing is repeated periodically rather than collected once and kept indefinitely.
Sideline tools are screening, not diagnosis
Brief sideline assessments are designed to be fast and sensitive, so they flag more athletes than are eventually diagnosed. That trade-off is deliberate.
Diagnosis is clinical and evolves over the following days, because symptoms frequently appear or worsen hours after the event rather than immediately.
The tools also depend on cooperation and on conditions that are rarely ideal. A crowded touchline with limited time is a poor setting for a memory task that requires concentration.
Why removal happens before certainty
Because assessment takes time and symptoms can be delayed, protocols remove any suspected case from play immediately and reassess later rather than clearing on the spot.
The reasoning is asymmetric risk: a missed day of competition is recoverable, while continuing to play with an unrecognised brain injury is not. Any suspected case needs medical assessment.
Playing on also raises the chance of a second impact while symptoms are active, and it leaves the decision to an athlete whose judgement is impaired by the injury being assessed.
