First nuts in glade (7)
I believe the answer is:
leading
'first' is the definition.
(leading can mean first or main)
'nuts in glade' is the wordplay.
'nuts' indicates anagramming the letters (nuts can mean crazy).
'in'+'glade'='inglade'
'inglade' anagrammed gives 'LEADING'.
(Other definitions for leading that I've seen before include "Main" , "in van" , "Most important; ahead" , "Foremost" , "Principal" .)