Opponent in Yemen beaten (5)
I believe the answer is:
enemy
'opponent' is the definition.
(I know that enemy is a type of opponent)
'yemen beaten' is the wordplay.
'beaten' is an anagram indicator (letters beaten up or destroyed).
'yemen' with letters rearranged gives 'ENEMY'.
'in' is the link.
(Other definitions for enemy that I've seen before include "Hostile opponent" , "Hostile person, foe" , "Time" , "Opposing force" , "Rival" .)