Out of left field

"Out of left field" is American slang meaning "unexpectedly", "odd" or "strange". The phrase came from baseball terminology referring to the area covered by the left fielder who has the farthest throw to first base. According to mlb.com there is another meaning: "The term 'way out in left field' is taken to mean 'crazy.'" Cook County Hospital (by the West Side Grounds, the Chicago Cubs first location under what is now the University of Illinois at Chicago College of Medicine) had a mental institution behind left field, (...) The bottom line is, patients could be heard yelling and screaming things at fans behind the left field wall.'" Variations include "out in left field" and simply "left field".