Compare prisoner with unfortunate start (8)
I believe the answer is:
contrast
'compare' is the definition.
(I've seen this before)
'prisoner with unfortunate start' is the wordplay.
'prisoner' becomes 'con' (abbreviation for 'convict').
'with' is a charade indicator (letters next to each other).
'unfortunate' indicates anagramming the letters.
'start' with letters rearranged gives 'trast'.
'con'+'trast'='CONTRAST'
(Other definitions for contrast that I've seen before include "Something completely different" , "No tracts by way of difference" , "Comparison to show differences" , "Distinction" , "Dissimilarity of things compared" .)