Caution in favour of conflict between opponents (8)
I believe the answer is:
forewarn
'caution' is the definition.
(I've seen this before)
'in favour of conflict between opponents' is the wordplay.
'in favour of' becomes 'for' (being for a particular cause).
'conflict' becomes 'war' (war is a kind of conflict).
'between' means one lot of letters goes inside another.
'opponents' becomes 'EN' (East and North players in the card game bridge).
'war' put inside 'en' is 'ewarn'.
'for'+'ewarn'='FOREWARN'
(Other definitions for forewarn that I've seen before include "Give previous notice" , "Point out coming danger" , "urge caution?" , "Notify of danger to come" , "alert" .)