break a leg

Good luck! as in Play well, Rob—break a leg! The origin of this imperative to a performer about to go onstage is unclear; it may have been a translation of the German Hals und Beinbruch (“Break your neck and leg”), also of unknown origin. Equally mysterious is the Italian equivalent, In bocca di lupe , “Into the mouth of the wolf.” [c. 1900]

Fracture one or more leg bones, as in She fell down the stairs and broke her leg in two places . [c. a.d. 1000]