Most concussions are the result of a direct blow to the head with a blunt object.

The brain normally floats within the skull surrounded by a clear fluid called cerebrospinal fluid. One of the functions of the CSF is to cushion the brain from injury. The fluid can absorb some of the shock associated with a head injury. If a blow to the head is sufficient, the CSF cannot compensate and the brain impacts the inner lining of the skull causing a bruise to the brain.