Subdued when mated, maybe (5)
I believe the answer is:
tamed
'subdued' is the definition.
('tame' can be a synonym of 'subdue')
'mated maybe' is the wordplay.
'maybe' is an anagram indicator.
'mated' with letters rearranged gives 'TAMED'.
'when' acts as a link.
(Other definitions for tamed that I've seen before include "Domesticated or subdued" , "Of animals, domesticated" , "Reined" , "now behaving himself?" .)