Caught, unfortunately, outside one Channel port (6)
I believe the answer is:
calais
'channel port' is the definition.
(I've seen this before)
'caught unfortunately outside one' is the wordplay.
'caught' becomes 'c' (cricket abbreviation).
'unfortunately' becomes 'alas' (I've seen this before).
'outside' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'alas' placed around 'i' is 'alais'.
'c'+'alais'='CALAIS'
(Other definitions for calais that I've seen before include "French port opposite Dover" , "A ferry port in northern France" , "Mary Tudor said it would be found "lying in my heart"" , "French port for ferry to England" , "Northern French port" .)