charley horse

Meanings

1. Synonym of cramp, a painful involuntary muscle contraction, particularly a strong cramp in the torso, arms, or legs.
2. A punch in the thigh.

Etymology

Uncertain, although first attested in American baseball slang of the 1880s, possibly related to cramps suffered by the pitcher Charles Gardner Radbourn, who was nicknamed "Old Hoss", or possibly from period use of Charlie as a generic name for horses similar to Rover for dogs and Felix for cats.