A man with a brace hit rock bottom (7)
I believe the answer is:
despair
'hit rock bottom' is the definition.
(thesaurus)
'a man with a brace' is the wordplay.
'a man' becomes 'Des'.
'with' is a charade indicator (letters next to each other).
'a brace' becomes 'pair' (a brace is a pair of something).
'des'+'pair'='DESPAIR'
(Other definitions for despair that I've seen before include "The feeling that nothing will turn out well" , "Lose or lack hope" , "Total loss of hope" , "gloom" , "Give up hope" .)