Frustrated participants in superhuman quest (6)
I believe the answer is:
manque
'frustrated' is the definition.
(French term meaning frustrated or failed)
'participants in superhuman quest' is the wordplay.
'participants in' indicates a hidden word.
'MANQUE' is hidden within 'superhuman quest'.
(Other definitions for manque that I've seen before include "Unsuccessful" , "Unfulfilled" , "Potential but unrealised, would-be" , "Frustrated in realising an ambition" , "Would-be; failed" .)