Half-baked crackers son leaves (5)
I believe the answer is:
inane
'half-baked' is the definition.
(both can mean foolish)
'crackers son leaves' is the wordplay.
'crackers' becomes 'insane' (similar in meaning).
'son' becomes 's'.
'leaves' suggests deleting specific letters.
'insane' with 's' taken away is 'INANE'.
(Other definitions for inane that I've seen before include "Vapid, fatuous" , "Fatuous, vacuous" , "Devoid of intelligence" , "Really stupid" , "Lacking sense, silly" .)