Depending upon the amount of force generated and the tear to the ligament severity can be graded from grade 1 to 3.
Grade 1: Stretching or slight tearing of the ligament with a little tenderness, swelling and stiffness.
Grade 2: A more severe sprain, but incomplete tear with mild pain, swelling and bruising.
Grade 3: A full tear of the ankle ligament and you feel instability while putting your weight, usually associated with a popping sound at the time of injury and other symptoms of grade 2.