Much has been written in recent years about the short- and long-term consequences of concussions sustained in sports, combat, and accidents. However, there appear to be no steadfast rules guiding the definition of concussion. Researchers investigated the signs, symptoms, and clinical histories used by athletic trainers to define concussion in individual college athletes engaged in contact sports. The investigators found a heterogeneous collection of acute clinical characteristics — a “concussion spectrum,” which they discuss.