Gangster in Sofia, corrupt in a short time (7)
I believe the answer is:
mafioso
'gangster' is the definition.
(I've seen this before)
'sofia corrupt in a short time' is the wordplay.
'corrupt' indicates anagramming the letters.
'in' means one lot of letters goes inside another.
'a short time' becomes 'mo' (slang abbreviation for 'moment').
'sofia' is an anagram of 'afios'.
'afios' placed within 'mo' is 'MAFIOSO'.
'in' acts as a link.
(Other definitions for mafioso that I've seen before include "Sicilian criminal" , "Member of a Sicilian mob" , "Italian criminal" , "Family man" , "One of the mob" .)