Out of Left Field - Phrase Meaning and the Idiom's Origins
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Example: Todd was thinking about going on a diet, when 'out of left field,' his wife came home and surprised him with a big box of donuts.
It's believed that this phrase comes from baseball, however, its exact origin, how it came
from baseball, is not clear.
In baseball, there are three outfield positions—the right fielder, the center
fielder, and the left fielder. If a ball has been hit hard enough to reach the outfielders, then they will attempt to catch the ball before it touches the ground, or they will try to quickly retrieve the ball and throw it back to the infield. So then, the term 'out of left field' would refer to the area that the left fielder is in.
One explanation as to the origin of this expression suggests this: If there is a base runner heading towards home plate, and the left fielder has the ball, he will throw it to the catcher at home plate in order to stop the runner from scoring. Since the base runner is sprinting towards home plate, he would be facing away from left field, so the ball would come from behind, thus it might surprise him. Perhaps this is how the phrase originated and later went on to be used outside of baseball to mean "to be surprised by something." Or perhaps not, because as was mentioned earlier, the precise origins of this phrase are unknown, this is simply one of a few explanations.