Crate smashed? Retaliate! (5)
I believe the answer is:
react
'retaliate' is the definition.
(I've seen this before)
'crate smashed?' is the wordplay.
'smashed?' indicates anagramming the letters.
'crate' is an anagram of 'REACT'.
(Other definitions for react that I've seen before include "Behave in response" , "What a chemical might do" , "Act as opponent" , "Hit back" , "Show opposition" .)