A sailor mostly caught one over in Corsican port (7)
I believe the answer is:
ajaccio
'corsican port' is the definition.
'ajaccio' can be an answer for 'port' (I've seen this before). I'm not sure about the 'corsican' bit.
'a sailor mostly caught one over' is the wordplay.
'sailor' becomes 'jack' (informal term for a sailor).
'mostly' means to remove the last letter (most but not all of the word).
'caught one over' becomes 'cio' (I can't justify this - if you can you should give a lot more credence to this answer).
'jack' with its last letter taken off is 'jac'.
'a'+'jac'+'cio'='AJACCIO'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for ajaccio that I've seen before include "Corsican city" , "island capital" , "Corsican town, Napoleon's birthplace" , "town on the Med" , "Corsican capital" .)