Symbol of remoteness

• Where Why is, in "Who's on First?"
• Site of Fenway Park's Green Monster
• Area patrolled by Jim Rice
• Out of __ (from nowhere)
• Position behind shortstop
• OUT IN __
• Source of bizarre ideas, so to speak
• The piece of ground in the outfield on the catcher's left
• Figuratively, whence some unexpected ideas

Wiktionary Word definitions in Wiktionary
a. From wikt:left field; off-the-wall