Introduce barmy cut (9)
I believe the answer is:
reduction
'cut' is the definition.
(thesaurus)
'introduce barmy' is the wordplay.
'barmy' indicates anagramming the letters.
'introduce' with letters rearranged gives 'REDUCTION'.
(Other definitions for reduction that I've seen before include "Introduce (anag) - decrease" , "cutback!" , "Introduce by way of discount" , "Drop in price" , "Lessening" .)