Although sprains of the hallux metatarsophalangeal (MTP) joint ligaments occur in barefooted martial arts athletes, few studies discuss the surgical treatments for lateral collateral ligament damage. We report herein a case of lateral collateral ligament repair for chronic hallux MTP joint instability. A 21-year-old male collegiate sumo wrestler injured his left hallux by snagging it on a sumo straw bale at 14 years of age. After entering university (4 years after the injury), he could no longer put weight on his foot at the left hallux; his athletic performance deteriorated, and he was referred to our department by his doctor. He had instability in the MTP joint of the left hallux, and magnetic resonance imaging revealed a tear in the attachment of the lateral collateral ligament to the metatarsal bone. Conservative treatment, such as taping, did not improve the symptoms; thus, surgery was performed, which consisted of passing a strong suture attached to the capsular ligament through a burr hole made in the metatarsal bone and fixing it to the burr-hole wall using an anchor. Postoperatively, the patient's joint instability improved, and he returned to competitive wrestling 4 months after surgery. He was able to put weight on his left hallux, and his athletic performance improved. The follow-up period after surgery was 2 years. In competitive sumo wrestling, hallux weakness and joint instability lead to a significant reduction in performance. Thus, ligament repair is an effective treatment for hallux MTP joint instability that cannot be treated by conservative means.