open stance (1921)

“At bat, [Jimmie] Tierney has what Ellsworth Giles might call an open stance–although Giles was quite a ballplayer himself a few years back.” Charles J. Doyle, “Buccaneer Pilot Seeking Pair of Emergency Men,” Gazette Times (Pittsburgh), January 6, 1921, p9
NOTE: E. Ellsworth Giles was a noted golfer and a write on golf. The term “open stance” was widely used to describe golfers long before it was applied to baseball.

No earliest use given in 2009 Dickson Baseball Dictionary