Runs into a very sad, crushed opponent (9)
I believe the answer is:
Here is my best explanation:
'opponent' is the definition.
('adversary' can be a synonym of 'opponent')
'runs into a very sad crushed' is the subsidiary indication.
'runs' becomes 'r' (cricket abbreviation).
'into' indicates putting letters inside.
'crushed' indicates anagramming the letters.
'averysad' anagrammed gives 'adversay'.
'r' going inside 'adversay' is 'adversary'.
(Other definitions for adversary that I've seen before include "Opponent, antagonist", "Opponent or enemy", "Foe, opponent", "Antagonist, opponent" and "Enemy or rival".)