In golf or other sports, to hit a ball poorly so it goes sideways instead of straight; or to stab someone with a shank (improvised knife).
From 'shank' (a thin leg or to hit poorly), from Old English 'sceanca' (leg, shin). In golf, developed as slang in the 1900s; in prison context, refers to using a shank weapon.
A 'shank' in golf is the worst feeling because it happens when you're trying hard—your muscles tense up and you hit the ball on the hosel (the socket connecting clubhead to shaft), sending it flying sideways embarrassingly.
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