An ankle sprain is a common injury in which one or more ligaments in the ankle are overstretched or torn. Ankle sprains are classified by the severity of the damage to the affected ligaments. In a Grade 1 sprain, the ligament is overstretched or slightly torn. This is often accompanied by mild pain, tenderness, swelling, and stiffness. A Grade 2 sprain is characterized by a more severe but incomplete tear that causes moderate pain, swelling, and bruising. It may become difficult to walk. A Grade 3 sprain occurs when the affected ligament has torn completely. With a Grade 3 sprain, pain, swelling, and bruising are usually severe and walking is usually impossible.