In horse racing, Lynd asserted that to wish a man luck is considered unlucky and so "You should say something insulting such as, 'May you break your leg! '" Thus, the expression could reflect a now-forgotten superstition (perhaps a theatrical superstition, though Lynd's 1921 mention is non-theatrical) in which directly wishing a person "good luck" would be considered bad luck, therefore an alternative way of wishing luck was employed. The urbane Irish nationalist Robert Wilson Lynd published an article, "A Defence of Superstition", in the 1 October 1921 edition of the New Statesman, a British liberal political and cultural magazine, regarding the theatre as the second-most superstitious institution in England, after horse racing.
The German-language term continues to mean "good luck" but is still not specific to the theatre.
For example, the Luftwaffe are reported as using the phrase Hals- und Beinbruch to wish each other luck and safety before a flight. Most commonly favored as a credible theory by etymologists and other scholars, the term was possibly a loan translation from the similar German phrase Hals- und Beinbruch, literally "neck and leg(bone) break", itself a loan translation from, and pun on, a Yiddish phrase (Yiddish: הצלחה און ברכה, romanized: hatsloche un broche, lit.'success and blessing', Hebrew: hatzlacha u-bracha), a wish for good luck, because of the Yiddish phrase's humorously similar pronunciation to the unrelated German phrase. Non-theatrical origins Yiddish-German pun theory
2.1 Other popular but implausible theories.