"Break a leg" is a well-known idiom in theatre which means "good luck." It is typically said to actors and musicians before they go out onto stage to perform.
The expression reflects a theatrical superstition in which wishing a person "good luck" is considered bad luck. The expression is sometimes used outside the theatre as superstitions and customs travel through other professions and then into common use.
There are several theories behind the etymology. All are heavily debated. The theories listed below are some of the more popular explanations.
The earliest known example in print refers to the title of a play from 1957. Naturally, the saying is much older for it to have been borrowed for a title and there is anecdotal evidence from theatrical memoirs and personal letters as early as the 1920s.
This theory is thought to be an extension of the Traditional Theory. For the curtain call, when actors bow or curtsy, they place one foot behind the other and bend at the knee, "breaking" the line of the leg. In theatre, pleased audiences may applaud in which time encore bows sometimes occur.
In Britain, the most common idea about the origin of the expression comes from tradition. Historians know from the time of King James I and Shakespeare's King's Men that actors would, on occasion, receive tips on top of their salaries. Rather than receiving tips directly from the company or theatre, tipping was left to the audience. During the final bows or curtain call, audiences would throw money, usually coins, onto the stage depending on how well they enjoyed the performance. In some bad performances they would throw rotten vegetables, but in the good cases, money. Actors would then "take a knee," effectively breaking their leg line, on stage and pick up the money. As a result, when a person wishes someone to "break a leg" it refers to wishing them success in their performance so in the end they would have to kneel down and collect a welcome tip. Theatre evolved and the tradition of tipping changed to one of throwing flowers on stage, as well as presenting flowers.
Full article can be found here: http://en.wikipedia.org/wiki/Break_a_leg
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Dancers, on the other hand, never say "break-a-leg" in place of "good luck" for obvious reasons. Back in our dancing days, we said "merde" instead. Does anyone still use that term?
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