Mad on nuts, swallowing large nut (6)
I believe the answer is:
almond
'nut' is the definition.
(almond is a kind of nut)
'mad on nuts swallowing large' is the wordplay.
'nuts' is an anagram indicator (nuts can mean crazy).
'swallowing' indicates putting letters inside.
'large' becomes 'l'.
'mad'+'on'='madon'
'madon' with letters rearranged gives 'amond'.
'amond' placed around 'l' is 'ALMOND'.
(Other definitions for almond that I've seen before include "Old man with nice nut" , "Edible nut" , "Nut often used in cake icing (6)." , "Oval-shaped edible seed" , "Oval-shaped nut" .)