CHARLEY HORSE - "Back in 1946 the 'Journal of the American Medical Association' published an article entitled 'Treatment of the Charley Horse,' rather than 'Treatment of Injury to Quadriceps Femoris.' This would indicate that 'charley horse' has been a part of formal English for at least 50 years. But did this term for a 'leg cramp' arise from a lame horse named Charley that pulled a roller across the infield in the Chicago White Sox ballpark in the 1890s? That's the old story, and there was such a horse, but the expression may have been printed several years before his baseball days, in 1888, to describe a ballplayer's stiffness or lameness. Another derivation that seems likely but hasn't been proved traces 'charley horse' to the constables, or Charleys, of 17th century England. According to this theory, 'Charleys,' for 'local police,' survived in America through the 19th century and because aching legs were an occupational disease among Charleys,' ballplayers suffering such maladies were compare to the coopers and said to be 'weary from riding Charley's horse.' " From the "Encyclopedia of Word and Phrase Origins" by Robert Hendrickson (Facts on File, New York, 1997).

From www.etymonline.com - baseball players' slang, 1888, origin obscure, probably from somebody's long-forgotten lame racehorse. From the Word Detective (http://www.word-detective.com/052699.html#charleyhorse) <--- excellent site for word/phrase origins "Yet another theory, and one that thankfully does not involve limping equines, holds that a player for Boston in the 1880's named Charley Radbourne was popularly known as "Old Hoss." As reported years later (1907) in a Washington Post article recently unearthed by slang expert Barry Popik, Radbourne was rounding the bases after hitting a home run in a game with Providence when his leg muscles seized up, bringing him painfully to the ground. Another player rushed to his aid, asking, "What's a mattah wit you, Charley Hoss?" And, says the Post, "from that day to this lameness in baseball players has been called 'Charley Hoss,' or 'Charles Horse.' True? Perhaps, but that story is probably not the last word on "charley horse." It seems that, at present, the actual origins are unknown. No mention of it in my copy of Brewer's. Bliss