Opponent has 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 anagramming the letters.
'yemen' anagrammed gives 'ENEMY'.
'has' acts as a link.
(Other definitions for enemy that I've seen before include "Foe, adversary" , "Yemen (anag.)" , "Opposing force" , "Rival" , "Hostile person, foe" .)