In this report we analyse a case of ischiatic tuberosity avulsion. A 15-year-old patient who came to our first aid department two days after a football match accident was treated conservatively and examined at month 1- 4, 6 and 12. In order to examine patient condition, a new index was formulated: the inability score index (ISI), which is based on hip range of motion and scales for rest, walking, running pain and compared to other parameters such as oedema area, fragment diastasis evaluated by X-ray and CT accordingly. ISI defines the inability as severe, moderate and mild. It guides the rehabilitative program in the right way. In this case, the patient was able to run softly after 35 days and to go back to the full agonist activity after 4 months. At the end of treatment the patient referred to the complete pain remission, full range of motion recovery and a good fracture consolidation. After 1 year we discuss about therapeutic strategies used and results obtained.