Many cheer, scattering chief foe (9)
I believe the answer is:
archenemy
'chief foe' is the definition.
(I've seen this before)
'many cheer scattering' is the wordplay.
'scattering' is an anagram indicator.
'many'+'cheer'='manycheer'
'manycheer' anagrammed gives 'ARCHENEMY'.
(Other definitions for archenemy that I've seen before include "Cheery man can be greatest foe" , "most dangerous opponent" , "Cheery man may be chief opponent" , "As Holmes regarded Moriarty" , "Chief foe" .)