Leaving group after ultimately futile sacrifice (8)
I believe the answer is:
offering
'sacrifice' is the definition.
(eg an offering to a god)
'leaving group after ultimately futile' is the wordplay.
I cannot really understand how this works, but
'leaving' could be 'off' (as in 'I'm off') and 'off' is present in the answer.
'group' could be 'ring' (a ring is a criminal organisation) and 'ring' is present in the answer.
A single letter 'e' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for offering that I've seen before include "Gift presented for acceptance" , "Contribution, sacrifice" , "Present" , "making a bid" , "Putting forward for acceptance or rejection" .)