Departing in defeat at long jump, perhaps (8)
I believe the answer is:
outbound
'departing' is the definition.
(synonyms)
'at long jump perhaps' is the wordplay.
'at' is a charade indicator (letters next to each other).
'long jump' becomes 'bound' (I've seen this before).
'perhaps' becomes 'out' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'bound' put after 'out' is 'OUTBOUND'.
'in defeat' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for outbound that I've seen before include "Going away" , "Leaving" , "Being in the process of departing" , "Headed away from home base" .)