Fatigue fracture of the pelvis is the form of fracture due to repetitive micro-stress accumulation, can be affected by a number of factors such as patient's nutritional status, biomechanics, social status and so on. Still there is no study about precise standard degree of external force that lead to stress fracture, but it may caused by compression force, traction force or complex force and others. Avulsion stress to ischial tuberosity or anterior superior iliac spine by attached muscle is known as the main factor for the avulsion fracture. This report will deal with 19 years old conscripted policeman who occurred ischial tuberosity avulsion fracture after training of 6-hour running for 5 days accompanying hip hyper-flexion motion. This reports aims to provide case study of stress fracture occurred after 5 days of exercise which is relatively short period who had no specific trauma history or pain.