A sprain is a stretch and/or tear of a ligament. A ligament is the fibrous band of connective tissue that joins the ends of two bones together. Ligaments stabilize and support the body's joints.An ankle sprain is caused by direct or indirect trauma that knocks the joint out of position, overstretches it or, in severe cases, ruptures the supporting ligaments. Typically, this injury occurs when an individual falls and lands on the side of the foot, or runs on an uneven surface. Symptoms of a sprain include pain, bruising, swelling, and inflammation. The individual oftentimes feels a tear or pop in the joint. In severe cases, this may make the joint nonfunctional. In other cases, where the sprain partially tears the ligament, some swelling may occur.