Hostility from states no one's backing (8)
I believe the answer is:
aversion
'hostility' is the definition.
(thesaurus)
'states no one's backing' is the wordplay.
'states' becomes 'avers' (to aver is to declare or state).
'one' becomes 'i' (Roman numeral).
'backing' says the letters should be written backwards.
'no'+'i'='noi'
'noi' reversed gives 'ion'.
'avers'+'ion'='AVERSION'
'from' is the link.
(Other definitions for aversion that I've seen before include "A strong dislike or repugnance" , "A feeling of dislike or reluctance" , "Extreme dislike" , "Feeling of intense dislike" , "serious dislike" .)