Match assistant (4)
I believe the answer is:
mate
I believe this clue is a double definition.
'match' is the first definition.
('mate' can be a synonym of 'match')
'assistant' is the second definition.
(I've seen this in other clues)
(Other definitions for mate that I've seen before include "couple" , "Team up with partner" , "China" , "Companion, wife" , "Friend; chess move" .)