Hopeful cop has energy, stopping decline (8)
I believe the answer is:
wannabee
'hopeful' is the definition.
(I know that hopeful can be written as wannabee)
'cop has energy stopping decline' is the wordplay.
I cannot really understand how this works, but
'cop' could be 'nab' (synonyms) and 'nab' is present in the answer.
'energy' could be 'e' (physics symbol as in E=mc2) and 'e' is found in the answer.
'decline' could be 'wane' (synonyms) and 'wane' is found in the leftover letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for wannabee that I've seen before include "who aspires to be different?" , "Aspirant" .)