Unknown; many unproven and widely debated theories exist. One of the most plausible is that it comes from Yiddish הצלחה און ברכה (hatslokhe un brokhe, “success and blessing”) through the heavy Ashkenazi Jewish influence in the American theater, via the misinterpretation in German as Hals- und Beinbruch (“neck and leg break”). The phrase in fact comes from Hebrew הַצְלָחָה וּבְרָכָה (hatzlakhá u-v'rakhá, “success and blessing”).
- (idiomatic) To perform well in a theatrical production or comparable endeavor.
- Go out there and break a leg tonight. Put on a great show!