Concussion is a brain injury that happens when an athlete collides with another person or the ground, or is hit by the ball or puck.
Getting hit in the head or body can make the brain crash against the inside of the skull, damaging the nerve fibers and causing concussive symptoms. You can’t see this kind of damage on an MRI or CT scan.
Sometimes symptoms come on right away, but other times they can take a few minutes or hours. The adrenaline of the game can mask an injury.