By a sudden movement, usually of the ankle, wrist sometimes (finger..) ligaments of the joint are overstretched, torn or ripped.
Ice, chilling, pressure dressings, rest. Higher laying reduces swelling and pain.
Little or no walking or supporting on it, but move the toes.

A muscular tear caused in the same manner is referred to as a strain.

Ligaments connect bone with bone. Tendons are a muscle extension, they connect muscles with bone (and are more stretchable). Did you know that cartilage has a coefficient of friction that is 5x smaller than ice!

Listening to a patient should not only be done by devices. (Remco Jonckers)