[Bob Kontak]

Direct from Wiki

A charley horse is a colloquial term typically used to refer to a muscle cramp or stiffness, particularly those of the calf, foot, leg, or more rarely, the arm. Some may use the term interchangeably with the term dead leg or thigh contusion, referring to a contusion caused by a physical blow to the leg or thigh.

The term came into use in the setting of baseball in the United States in the 1880s, though its exact origin is uncertain.

https://en.wikipedia.org/wiki/Charley_horse