charley horsechar·ley horse
Informal a cramp or soreness in a muscle, specif. of the thigh, caused by strain
Origin of charley horseballplayers' slang, c. 1888; probably with reference to a lame racehorse
A cramp or stiffness in a muscle, especially of the upper leg, caused by injury or excessive exertion.
Origin of charley horseOriginally baseball slang, of unknown origin.
The term may date back to American slang of the 1880s, possibly from the pitcher Charlie "Old Hoss" Radbourn who is said to have suffered from cramps.