This article explains the various stresses (tensile, compressive, and shearing) that can affect the brain, and how they may produce the different types of brain injury. The biomechanical forces and dynamics that produce coup versus contra coup injury are covered, as are the common intracranial athletic head injuries, i.e. concussion and the various intracranial haematomas (epidural, subdural, subarachnoid and intracerebral). Though less common in occurrence, because their outcome is so catastrophic, space is also devoted to the recognition, the treatment and (especially in the latter case) the prevention of the malignant brain oedema syndrome of the adolescent and the second impact syndrome of the adult. A major emphasis of this paper is the recognition of the 3 grades of cerebral concussion and the delineation of clear guidelines as to when it is safe to return to collision sports after sustaining such injuries, for the first, second or third time during a given season. Clear guidelines are also presented as to when to discontinue collision sport competition for the remainder of the season after multiple concussions. Because of the concern for the second impact syndrome, the requirement to never allow an athlete with postconcussion syndrome symptoms to return to competition is emphasised. Also covered is the prevention of head injuries, which sports are at greatest risk, and the need for additional research on the cumulative effects of concussion.