Withdraw as bear gets depressed (5,4)
I believe the answer is:
'withdraw' is the definition.
'bear gets depressed' is the wordplay.
'bear' becomes 'stand' (synonyms).
'gets' is a charade indicator (letters next to each other).
'depressed' becomes 'down' (synonyms).
'as' acts as a link.
(Other definitions for stand down that I've seen before include "Withdraw from post or competition" , "not to be a candidate" , "Withdraw as from competition, be seated" , "Withdraw voluntarily, from job or competition" , "Leave the witness box" .)