Concussion of the brain

Anatomy: The brain is surrounded by the membrane of the brain (meninx) and protected by the cranial bones.

Cause: With a violent blow or shaking of the head, the brain can collide against the cranial bones with such a force that bleeding can occur, or fluids can seep, on to or in to the surface of the brain.

Symptoms: Headache, general uneasiness, nausea, visual disturbance, drowsiness, increasing remoteness, unconsciousness, convulsions and in worst case, death (article). In the rare cases where a fatality occurs in sport due to a blow to the head, it is often caused by incurring two head injuries in the same match.

Examination: All athletes who receive a blow to the head and subsequently complain of uneasiness, visual disturbance or haziness should immediately cease further sport and undergo medical examination. 
All head injuries must be taken very seriously! (article)

Treatment: Rest and relief until the symptoms have abated (article). It is naturally highly inappropriate, and can be extremely hazardous, to take head ache pills in order to continue sports activity.

Rehabilitation: Rest and relief until the symptoms have abated. Training can subsequently be cautiously resumed, but should be stopped immediately if symptoms are experienced again (for example head ache).
Also read rehabilitation, general.

Special: More widespread use of helmets in different sports will unquestionably reduce the number of concussions and after effects thereof. It is imperative that athletes with head injuries which have brought about groggy moments are removed from the sports activity and not permitted to resume until the symptoms have gone during the following days (article 1), (article 2).