A groin pull is an injury to the muscles (a muscle strain) of the inner thigh. The groin muscles, called the adductor muscle group, consists of six muscles that span the distance from the inner pelvis to the inner part of the femur (thigh bone).
These muscles pull the legs together and help with other movements of the hip joint. The adductor muscles are important to many types of athletes including sprinters, swimmers, soccer players, and football players.
When a muscle is strained, the muscle is stretched too far. Less severe strains pull the muscle beyond their normal excursion. More severe strains tear the muscle fibers, and can even cause a complete tear of the muscle. Most commonly, groin pulls are minor tears of some muscle fibers, but the bulk of the muscle tissue remains intact.