A concussion is any injury to the brain that disrupts normal brain function typically on a temporary basis. Concussions are usually caused by a blow or jolt to the head but may occur from a hit to the body that produces a reflex force to the head.
The symptoms of a concussion range from subtle to obvious and usually happen right after the injury but some may take hours to a few days to develop. Athletes who have had concussions may report feeling normal before their brain has fully recovered. With most concussions, the player is not knocked out or unconscious.