The most widely accepted theory for concussion is that acceleration–deceleration forces cause the injury. Sudden and rapid acceleration of the head from a position of rest makes the head move in several directions. The brain, protected by cerebrospinal fluid (CSF) and cushioned by various brain attachments, moves more slowly than the skull. The lag between skull movement and brain movement causes stretching of veins connecting the subdural space (the space beneath the dura mater of the brain) to the surface of the brain, resulting in minor disruptions of the brain structures. Common causes of concussion are a fall, a motor vehicle crash, a sports-related injury, and a punch to the head.