Charley horse is a non specific term, typically used to refer to a muscle cramp, stiffness, or contusion. Generally it is used for the thigh, calf, or foot, or more rarely, the arm. The term may be used interchangeably with dead leg or thigh contusion, referring to an injury 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.
The first known written use of the term was in 1886 in The Boston Globe. The origination has been attributed to two baseball players, Jack Glasscock and Joe Quest. However, its exact origins are unknown.