Fighter on parole faces a tough problem (7)
I believe the answer is:
opposer
'fighter' is the definition.
Both the answer and definition are singular nouns.
Perhaps they are linked in a way I don't understand?
'on parole faces a tough problem' is the wordplay.
'on parole' becomes 'op' (this could be a standard abbreviation which I don't know about).
'faces' is a charade indicator (letters next to each other) (some letters face or meet others).
'a tough problem' becomes 'poser' (I've seen this in another clue).
'op'+'poser'='OPPOSER'
Can you help me to learn more?
(Other definitions for opposer that I've seen before include "One offering resistance" , "Propose to challenger" , "One who takes on" , "The one against the motion" , "Person against the motion" .)