Squash bullies' leader - complete lunatic (9)
I believe the answer is:
butternut
'squash' is the definition.
(butternut squash is a kind of squash)
'bullies' leader complete lunatic' is the wordplay.
'leader' suggests taking the first letters.
'complete' becomes 'utter' (I've seen this before).
'lunatic' becomes 'nut' (I've seen this before).
The first letter of 'bullies' is 'b'.
'b'+'utter'+'nut'='BUTTERNUT'
(Other definitions for butternut that I've seen before include "Variety of pumpkin" , "sort of a squash" , "Wood" , "species of tree" .)