Sudden attack has one leaving Italian city (4)
I believe the answer is:
turn
'sudden attack' is the definition.
'turn' can be an answer for 'attack' (thesaurus). I'm not sure about the 'sudden' bit.
'one leaving italian city' is the wordplay.
'one' becomes 'I' (Roman numeral).
'leaving' suggests deleting specific letters.
'italian' becomes 'it' (abbreviation for Italian).
'city' becomes 'urn' (I am not sure about this - if you are sure you should believe this answer much more).
'it' with 'i' taken away is 't'.
't'+'urn'='TURN'
'has' is the link.
Can you help me to learn more?
(Other definitions for turn that I've seen before include "Rotate for a performer's act" , "Revolve - go off" , "Go; spin (cricket)" , "Rotate - go" , "change for Autumn" .)