Scoundrel crazy about Europe's largest port (9)
I believe the answer is:
rotterdam
'europe's largest port' is the definition.
(I've seen this in another clue)
'scoundrel crazy about' is the wordplay.
'scoundrel' becomes 'rotter' (both can mean a nasty person).
'crazy' becomes 'mad' (synonyms).
'about' says the letters should be written backwards.
'mad' backwards is 'dam'.
'rotter'+'dam'='ROTTERDAM'
(Other definitions for rotterdam that I've seen before include "Netherlands port" , "city abroad" , "foreign city" , "Major world seaport at the mouth of the Meuse" , "Major North Sea port - tarred tom (anag)" .)