Fix match? Sad (3,4)
I believe the answer is:
tie down
'fix' is the definition.
(I've seen this before)
'match? sad' is the wordplay.
'match?' becomes 'tie' (I've seen this before**).
'sad' becomes 'down' (I've seen this before).
'tie'+'down'='TIE DOWN'
(Other definitions for tie down that I've seen before include "Restrain with ropes" , "Fix; bind by conditions" , "Bind by conditions - to widen (anag)" , "Restrict" .)