Bully guys between two hills (9)
I believe the answer is:
tormentor
'bully' is the definition.
(I've seen this before)
'guys between two hills' is the wordplay.
'guys' becomes 'men' (guy can mean a man).
'between' is an insertion indicator.
'two' shows that letters should be duplicated.
'hills' becomes 'tor' (tor is a kind of hills).
'tor' duplicated is 'tortor'.
'men' inserted inside 'tortor' is 'TORMENTOR'.
(Other definitions for tormentor that I've seen before include "Inflictor of pain or anguish" , "Crossword setter maybe" , "One harassing" , "cause of suffering" , "One causes pain" .)