"A groin strain is a tear or rupture to any one of the adductor muscles resulting pain in the inner thigh. Groin injuries can range from very mild to very severe injuries that are completely debilitating.

Groin strains are usually occur when sprinting or changing direction quickly or during rapid movements of the leg against resistance such as kicking a ball. Over stretching the muscle such as in martial arts high kicks can also cause a torn adductor muscle."

http://www.sportsinjuryclinic.net/sport-injuries/hip-groin-pain/groin-strain