Opposing a profit on site, oddly (7)
I believe the answer is:
against
'opposing' is the definition.
(thesaurus)
'a profit on site oddly' is the wordplay.
'profit' becomes 'gain' ('gain' can be a synonym of 'profit'**).
'on' means one lot of letters go next to another.
'oddly' indicates alternate letters.
The alternating letters of 'site' are 'st'.
'a'+'gain'+'st'='AGAINST'
(Other definitions for against that I've seen before include "In conflict with" , "Not supporting" , "In disagreement with" , "Disapproving of" , "Opposed" .)