Out of Left Field -- phrase origin

Today's fun fact?

An unusual idea would be "something out of left field" in American 
idiom.  This is obviously a baseball-based expression, but why left 
field? Why not use center field, which is usually farther out?

http://www.chicagotribune.com/features/lifestyle/chi080515west-side-cubs_gfx,0,7217375.graphic
The Tribune claims that this phrase originated from a psychiatric 
hospital located just beyond the left field wall of the West Side 
Grounds -- the baseball stadium where the Cubs played through 1915, 
when they moved to Weeghman Park, now Wrigley Field.

-- 
Mike Kruger
"You have to be careful if you are reckless." - Richard M. Daley