Many of us at sometime in our lives have had that painful balling up of thigh, calf, or foot muscle which can be extremely painful.
How did these muscle cramps get the name Charley Horse?
From this site:
Yep! It’s almost certainly a baseball term. I made William Safire’s December 7th column On Language in the NY Times Magazine with the earliest cite found so far–August, 1886. It certainly originated before that date, and as more newspapers are digitized, we’ll push the first citing back a bit farther. Perhaps some day we may actually find out if it originated in a single location, and whether it referred to anyone in particular. But for now, it’s mysterious.