Once more a good man is in opposition (7)
I believe the answer is:
against
'is in opposition' is the definition.
(I've seen this before)
'once more a good man' is the wordplay.
'once more' becomes 'again' ('again' can be a synonym of 'once more').
'a good man' becomes 'st'.
'again'+'st'='AGAINST'
(Other definitions for against that I've seen before include "Opposing" , "Disapproving of" , "Versus - in contact with" , "Placed in direct contact with" , "In competition with" .)