Hostility? A good man is not provoked (10)
I believe the answer is:
antagonism
'hostility?' is the definition.
(I know that antagonism is a type of hostility)
'a good man is not provoked' is the wordplay.
'good' becomes 'g' (abbreviation).
'provoked' indicates anagramming the letters.
'g'+'man'+'is'+'not'='gmanisnot'
'gmanisnot' is an anagram of 'ntagonism'.
'a'+'ntagonism'='ANTAGONISM'
(Other definitions for antagonism that I've seen before include "Active opposition" , "Active hostility" .)