“Out in left field” (“Out of left field”)

Entry in progress—B.P.
 
Wikipedia: Left fielder
Out of left field
The phrase “out of left field” is popular vernacular (first attested in 1961) meaning “wildly unrelated to the subject being discussed”, and “out in left field” means “a little crazy”. One theory is that this refers to the popularity of seats in right field at Yankee Stadium while Babe Ruth was playing that position; buying a seat in left field would have been “stupid”. Another theory is that this arose at Chicago’s second West Side Park, home of the Chicago Cubs from 1893 to 1915. After the Cubs moved to what is now Wrigley Field, the West Side Park property eventually became the home of the University of Illinois College of Medicine. The U of I built its Neuropsychiatric Institute building in what had been left field. A third theory comes directly from experience of players. A runner attempting to score at home has his back to the left field, thus a throw to the plate coming from left field can arrive as a surprise to the runner.
 
YourDictionary.com
out in left field idiom
Also, out of left field. Eccentric, odd; also, mistaken. For example, The composer’s use of dissonance in this symphony is way out in left field, or His answer was out of left field; he was totally wrong. This idiom refers to baseball’s left field but the precise allusion is disputed. Among the theories proposed is that in some ballparks the left field wall is farther from the batter than the wall in right field. Another is that in early ballparks, left field was often larger than right field and therefore was home to more lost balls and general confusion. [Mid-1900s] Also see far out.
 
(Oxford English Dictionary)
left field (Baseball): the part of the outfield to the left of the batter as he faces the pitcher; also, a fielder in this position; also fig., a position away from the centre of activity or interest
1961 Amer. Speech XXXVI. 147 Out in left field, disoriented, out of contact with reality.
1970 Time 9 Mar. 19 An increasing number of candidates are emerging from leftfield to give voters surprising options.
1974 Publishers Weekly 11 Mar. 48/3 Novak’s use of religious metaphor may put him in left field (Reinhold Niebuhr was there before him).
 
26 October 1934, Oakland (CA) Tribune, “The National Whirligig” by George Durno, pg. 41, col. 1:
Any New Dealer so brash in the interim as to start announcing new policies or taking controversial action in connection with those existing probably would wind up in left field without a glove.
 
2 September 1936, Lowell (MA) Sun, pg. 2, col. 4:
The press was kept out in left field without a glove.
 
16 August 1946, New York (NY) Times, pg. 4:
“Comrade Connolly is, as usual, out in left field,” Mr. Flynn said in reply.
 
18 November 1951, New York (NY) Times, pg. 46:
“Webster’s is out in left field all by itself,” Mr. Bills declared.
(Merriam-Webster’s defining of a word, compared to OED and others—ed.)
 
15 March 1953, New York (NY) Times, pg. 19:
“What I mean is simply that our subcommittee has no intention of getting caught out in left field when the next batter may swing from the other side of the plate.”
 
18 September 1960, New York (NY) Times, pg. 1:
“We’ve been left out in left field,”