Part of flight from southern Italy caught by seaman (5)
I believe the answer is:
stair
'part of flight' is the definition.
(as in a flight of stairs)
'southern italy caught by seaman' is the wordplay.
'southern' becomes 's' (abbreviation).
'italy' becomes 'i'.
'caught by' indicates putting letters inside.
'seaman' becomes 'tar' (Jack Tar is an informal term for a sailor).
'i' put into 'tar' is 'tair'.
's'+'tair'='STAIR'
'from' is the link.
(Other definitions for stair that I've seen before include "Component of flight" , "something of a case" , "Support on which to step" , "single step in a series" , "Set of steps" .)