Soldier spoiled aim with the thing in Italian city (10)
I believe the answer is:
militiaman
'soldier' is the definition.
(militiaman is a kind of soldier)
'spoiled aim with the thing in italian city' is the wordplay.
'spoiled' indicates anagramming the letters.
'with' means one lot of letters go next to another.
'the thing' becomes 'it'.
'in' is an insertion indicator.
'italian city' becomes 'milan' (I've seen this before).
'aim' anagrammed gives 'iam'.
'iam' put after 'it' is 'itiam'.
'itiam' placed into 'milan' is 'MILITIAMAN'.
(Other definitions for militiaman that I've seen before include "Member of civilian force" , "As fighter" , "Such as a member of the US National Guard" , "reservist" .)