Underdog contender “Rocky” couldn’t triumph over Broadway, where soft sales have led producers to post an Aug. 17 closing notice for the big-budget musical based on the Oscar-winning film.

The early closing, capping the run at just six months, dashes the high hopes inspired by a musical that seemingly had the potential for cross-demographic success with a plot that, as both a love story and an underdog sports tale, could appeal both to women (who make the majority of Broadway ticket purchases) and to men. The Shubert Organization, Broadway’s biggest landlord, slotted the show into one of the company’s prime houses, the Winter Garden, where “Cats” played out its long run and “Mamma Mia!” became a smash.

But despite a successful German-language premiere in 2012 in Hamburg, Germany — where “Rocky” is still playing — Broadway audiences never took the bait. A savvy and sophisticated marketing campaign couldn’t overcome the cognitive dissonance that American theatergoers felt in imagining the laconic bruiser Rocky burst out into song.

Following the musical’s March 13 opening, reviews in the New York press were mixed, with positive notices balanced by more downbeat assessments in some prominent outlets. The Tony Awards nominators left the title out of the best musical race, and not even a flashy number on the Tony telecast, showcasing the signature spectacle of the tuner’s finale, could turn up the heat at the box office.

Weekly sales have, for the most part, hovered in the $700,000 range, which is far less than would be required for a large-scale musical with high weekly running costs to push through to recoupment. The technically ambitious show, encompassing a mobile boxing ring that descends into the orchestra during the climactic final sequence, weighed in at a reported $16.5 million in capitalization. Little of those costs will have been made back from the musical’s soft sales.

The closing represents a disappointment for lead producer Stage Entertainment USA, the American branch of European theatrical giant Stage Entertainment. A heavyweight producer of theatrical fare abroad, Stage has yet to establish an enduring Broadway hit. The company’s production of  “Sister Act” ran in New York for less than 18 months, while last season’s “Big Fish” sank even quicker.