Charley Horse (1886)

“Ely is still suffering from a sore arm, and Reccius has what is known by ball players as ‘Charley Horse,’ which is a lameness in the thigh, caused by straining the cord.” Jim Hart [manager of the Louisville Colonels], “From Manager Hart” (letter to the paper), Louisville Courier-Journal, March 21, 1886, p10.

Previous earliest use (Dickson Baseball Dictionary, 3rd edition, 2009):
1886.  “Pfeffer, Anson and Kelly are so badly troubled with ‘Charley horse’ that there are times when they can hardly walk.” (The Boston Globe, July 17).