Tip off pro: create conflict between opponents (8)
I believe the answer is:
'tip off' is the definition.
(I've seen this before)
'pro create conflict between opponents' is the wordplay.
'pro' becomes 'for' (I've seen this before).
'create' says to put letters next to each other.
'conflict' becomes 'war' (war is a kind of conflict).
'between' indicates putting letters inside.
'opponents' becomes 'en' (I've seen this in other clues).
'war' inserted into 'en' is 'ewarn'.
(Other definitions for forewarn that I've seen before include "Caution in advance" , "Point out coming danger" , "Tip off" , "alert" , "Give advance notice" .)