Opposing a good person pocketing profit (7)
I believe the answer is:
against
'opposing' is the definition.
(thesaurus)
'a good person pocketing profit' is the wordplay.
'good person' becomes 'st' (saint).
'pocketing' is an insertion indicator.
'profit' becomes 'gain' ('gain' can be a synonym of 'profit').
'a'+'st'='ast'
'ast' enclosing 'gain' is 'AGAINST'.
(Other definitions for against that I've seen before include "Opposed" , "In contrast to; touching" , "Con" , "Anti, touching" , "Not supporting" .)