Poem about fool in Black Sea port (6)
I believe the answer is:
odessa
'black sea port' is the definition.
(Ukrainian port on the Black Sea)
'poem about fool' is the wordplay.
'poem' becomes 'ode' (ode is a type of poem).
'about' shows that the letters should be reversed in order.
'fool' becomes 'ass' (both can mean a stupid person).
'ass' back-to-front is 'ssa'.
'ode'+'ssa'='ODESSA'
'in' acts as a link.
(Other definitions for odessa that I've seen before include "Do seas come into Ukrainian city?" , "Ukrainian naval base" , "Ukrainian Black Sea port" , "Battleship Potemkin mutiny port" , "Seaport" .)