Fight to the death, as sleuth revealed (6)
I believe the answer is:
hassle
'fight' is the definition.
(I know that hassle is a type of fight)
'the death as sleuth revealed' is the wordplay.
'revealed' indicates the answer is hidden within the clue (I've seen 'revealing' mean this).
'HASSLE' is hidden in the letters of 'the death as sleuth'.
'to' acts as a link.
(Other definitions for hassle that I've seen before include "Difficulty - dispute" , "Harass; pester" , "Pester (colloq.)" , "Harass - grief" , "problem" .)