origin of charley horse?

What is the origin of the expression, “charley horse”?

It does mean a painful cramp in the calf muscle, I believe.

According to JE Lighter, American Slang, it is originally from baseball.

He cites 1888 in AS American Speech "I could dance in those days, because, you see, I never was bothered with “Charley Horse.”

All of his pre-1930 cites are from baseball.

He says the origin is obscure.

From Philoman’s Homepage who claims the following…

“The phrase first appeared in the 1880s. No one knows the exact origin but there are two fairly popular theories. The first, which is probably not true, relates the phrase to a race horse named Charley or Charlie who was allegedly lamed by the affliction.
A more likely story is that the phrase referred to a baseball player named Charley Radbourne who fell prey to a muscle cramp during a game in 1880. Radbourne’s nickname was “Old Hoss.””