Knife for staff eating the bananas (7)
I believe the answer is:
machete
'knife' is the definition.
(machete is a kind of knife)
'staff eating the bananas' is the wordplay.
'staff' becomes 'mace' (mace is a kind of staff).
'eating' is an insertion indicator.
'bananas' indicates an anagram (informal term for mad).
'the' anagrammed gives 'het'.
'mace' enclosing 'het' is 'MACHETE'.
'for' is the link.
(Other definitions for machete that I've seen before include "Broad heavy knife used in S America" , "Cheat me over broad heavy knife used in jungle" , "Heavy knife used as weapon" , "Large heavy knife for cutting vegetation" , "Teach me with large jungle knife" .)