Equip a Baltic port (4)
I believe the answer is:
riga
'baltic port' is the definition.
(I've seen this in another clue)
'equip a' is the wordplay.
'equip' becomes 'rig' (rigging is a kind of equiping).
'rig'+'a'='RIGA'
(Other definitions for riga that I've seen before include "Fix a rig up here for the Latvians" , "port in Latvia" , "Latvian port" , "Latvian capital" , "A rig in Latvia" .)