Nuts mother served up (3)
I believe the answer is:
mad
'nuts' is the definition.
(informal term)
'mother served up' is the wordplay.
'mother' becomes 'dam' (female parent of an animal).
'served up' says the letters should be written in reverse (in a down clue, going upwards).
'dam' backwards is 'MAD'.
(Other definitions for mad that I've seen before include "Angry or insane" , "Aberrant" , "Crazy" , "Crazed" , "Idiotic" .)