BACKGROUND Hip avulsion fractures occur mostly during adolescence when actions such as kicking or running cause forceful contraction of attached muscle. Osteochondroma is benign tumor that mostly occurs at the metaphysis of a long bone, being usually asymptomatic. CASE SUMMARY A 15-year-old patient experienced feeling and sound of a break while kicking a ball in soccer game three years prior to his visit to our hospital. A simple X-ray revealed an avulsion fracture of the apophysis of the anterior inferior iliac spine (AIIS). Later in the follow-up X-ray, a palpable mass was found and demonstrated by magnetic resonance imaging to be a pedunculated osteochondroma in the superolateral aspect of the AIIS. For surgical treatment, we performed osteotomy for surgical excision and excisional biopsy. A mass with smooth surface and an unclear superolateral AIIS border was found intraoperatively. Pathologic exam showed definite diagnosis of osteochondroma. Postoperatively, discomfort during hip flexion was improved, and the hip joint range of motion during walking was recovered at the last follow-up, which was three weeks after the surgery. CONCLUSION This is a rare case to demonstrate relevant previous trauma history prior to the formation of osteochondroma.