Backing the Italian supporter making sign (5)
I believe the answer is:
libra
'sign' is the definition.
(sign of the zodiac)
'backing the italian supporter' is the wordplay.
'backing' is a reversal indicator.
'the italian' becomes 'il' ('the' in Italian).
'supporter' becomes 'bra' (a bra gives support to breasts).
'il' back-to-front is 'li'.
'li'+'bra'='LIBRA'
'making' is the link.
(Other definitions for libra that I've seen before include "House" , "Someone born between September 23 and October 22" , "Zodiacal sign" , "Scales star sign" , "The Scales in astrology" .)