A 13-year-old girl experienced a fall during gym class that caused immediate unresponsiveness and death. The lone witness reported that the decedent lost her balance as she approached a hurdle and fell, striking her head on a crossbar of the hurdle near the ground. Autopsy revealed no external injury. Internal injury that could be demonstrated anatomically was confined to a contusion within the right semicapitis muscle at the base of the skull. In the absence of an anatomic cause of death, possible explanations of the death include a cardiac dysrhythmia, a vasovagal stimulus, and diffuse axonal injury caused by a concussive force to the junction of the medulla and spinal cord. Animal studies have shown that severe concussion can cause death via profound autonomic dysfunction without leaving anatomic evidence of injury, and that the essential component of concussion is an element of rotational injury to the brain. The authors believe that the blow to the neck caused this death by the transmission of a concussive force through the reticular activating system. The prompt work of police in distinguishing the lone witness from several people in the area who thought they knew what had happened was essential for diagnosis. On reaching our conclusions, the authors notified first the family, then the superintendent of the school system, and finally the news media. The authors told each party in turn that they would be contacting the others.