Here, we present a rare case of a preadolescent boy with a prominent bony bump on the femoral neck. The main histological feature was concordant with a reactive osteochondromatous lesion possibly induced by repetitive microtrauma, probably because of overtraining as a soccer goalkeeper. The nature of this pathological change is consistent with the growth of a cam deformity. Especially in the preadolescent age group, we should note that repetitive use of the same joint kinematics may induce a prominent cam deformity.