be a surprise hit

「（映画などで）驚きのヒット」。

The New York Timesの記事、'Graying Audience Returns to Movies' By BROOKS BARNES and MICHAEL CIEPLYから。

'LOS ANGELES — Hollywood and older Americans have never had much use for each other. The 50-plus crowd doesn’t go to opening weekends or buy popcorn; a youth-obsessed Hollywood has happily ignored them.

But in the last few months an older audience has made a startling reassertion of its multiplex power. “True Grit,” “The King’s Speech,” “The Fighter,” “Black Swan” — all movies in contention for a clutch of Oscars on Sunday — have all been surprise hits at the box office.'