Bananas all tear on the side (7)
I believe the answer is:
lateral
'on the side' is the definition.
(lateral means located on the side)
'bananas all tear' is the wordplay.
'bananas' is an anagram indicator (informal term for mad).
'all'+'tear'='alltear'
'alltear' with letters rearranged gives 'LATERAL'.
(Other definitions for lateral that I've seen before include "Towards the side" , "This kind of sideways thinking does not use conventional logic" , "Of, at or towards the sides (7)" , "belonging to the side" , "Sort of thinking" .)