“A charley horse is a popular North American colloquial term for a painful contusion (bruise) of the quadriceps muscle of the anterior or lateral thigh that commonly results in a muscular hematoma and sometimes several weeks of pain and disability. Such an injury is known in the UK and many Commonwealth countries (and also in the U.S.) as a dead leg. In Australia it is also known as a corked thigh or “corkie”. It often occurs in sports when an athlete is struck by an opponent’s knee, in a manner like the kick of a horse, perhaps the reason for its name….It could also be as simple as not enough magnesium or potassium, or too much calcium.” ~Wikipedia Simple It’s a bruise, or a cramp. :)