An idiot seen in foreign port (7)
I believe the answer is:
antwerp
'foreign port' is the definition.
'Antwerp' can be an answer for 'port' (Belgian port). I'm not sure about the 'foreign' bit.
'an idiot' is the wordplay.
'idiot' becomes 'twerp' (both can mean a fool).
'an'+'twerp'='ANTWERP'
'seen in' acts as a link.
Can you help me to learn more?
(Other definitions for antwerp that I've seen before include "Belgian city/port" , "North Sea port" , "New part of Dutch city" , "War-damaged city" , "Major European port" .)