A 39-year-old woman sustained a forced dorsiflexion injury to the left great toe while pivoting to the right during tennis activity. Posteromedial ankle pain was reproduced with active plantarflexion and passive dorsiflexion of the great toe and, to a smaller extent, the lesser toes. Symptoms persisted for 9 months despite nonoperative treatment. Magnetic resonance imaging 5 months after injury revealed evidence of fluid surrounding the flexor hallucis longus (FHL) tendon. Operative findings 9 months after injury included scar tissue and tenosynovitis of the FHL and flexor digitorum longus tendon sheaths, with impingement of distal FHL muscle fibers and a longitudinal split tear (partial rupture) of the FHL tendon. Tenolysis, tenosynovectomy, excision of the distal muscle fibers, and repair of the partial tendon rupture were performed, resulting in resolution of symptoms. Partial rupture of the FHL tendon as a single-impact injury, or in activity other than ballet, has not been documented previously.