In briefThe known risk of second impact syndrome (SIS) in football has elevated the importance of postconcussion and precompetition exams of injured football players. Six case reports demonstrate that the same mechanism of injury—minor head trauma in a player who still has symptoms from a previous concussion—can cause second impact syndrome in any contact sport. It is important to monitor postconcussion symptoms, which include headache, light-headedness, and impaired consciousness. Return-to-play guidelines for football and boxing provide a basis for making safe activity recommendations for other sports.