Conflict interrupting river crossing in advance (7)
I believe the answer is:
forward
'in advance' is the definition.
(thesaurus)
'conflict interrupting river crossing' is the wordplay.
'conflict' becomes 'war' (war is a kind of conflict).
'interrupting' is an insertion indicator.
'river crossing' becomes 'ford' (I've seen this before).
'war' placed within 'ford' is 'FORWARD'.
(Other definitions for forward that I've seen before include "left-winger, maybe" , "Attacker" , "Dispatch" , "Attacking player" , "advance" .)