Opponent in Yemen confused (5)
I believe the answer is:
enemy
'opponent' is the definition.
(I know that enemy is a type of opponent)
'yemen confused' is the wordplay.
'confused' indicates an anagram.
'yemen' with letters rearranged gives 'ENEMY'.
'in' is the link.
(Other definitions for enemy that I've seen before include "Rival" , "is against us" , "Yemen (anag.)" , "Armed adversary" , "Antagonist" .)