Stratagem sure to fail (4)
I believe the answer is:
ruse
'stratagem' is the definition.
(a ruse is a stratagem or ploy)
'sure to fail' is the wordplay.
'to fail' indicates anagramming the letters (letters go wrong or fail).
'sure' is an anagram of 'RUSE'.
(Other definitions for ruse that I've seen before include "Sure to be a plot" , "Cunning plan" , "Trick, stratagem" , "Ploy, artifice" , "Cunning scheme" .)