Smash hit (11)
I believe the answer is:
blockbuster
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">smash hit</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for blockbuster that I've seen before include "best seller?" , "Landmine" , "Smash hit" , "Very successful book, movie etc" , "Commercial success" .)