Unfriendly agent going round a secret port (7)
I believe the answer is:
stroppy
'a secret port' is the definition.
Both the answer and definition are adjectives. Maybe they are linked in a way I don't understand?
'unfriendly agent going round' is the wordplay.
'unfriendly' becomes 'trop' (I can't explain this - if you can you should believe this answer much more).
'agent' becomes 'spy' (spy is a kind of agent).
'going round' is an insertion indicator (some letters go around others).
'trop' inserted inside 'spy' is 'STROPPY'.
Can you help me to learn more?
(Other definitions for stroppy that I've seen before include "Obstreperous" , "Bolshie" , "Difficult" , "Awkward to handle" , "Bad-tempered, argumentative" .)