In pieces, since inferior (7)
I believe the answer is:
asunder
'in pieces' is the definition.
(asunder means torn apart)
'since inferior' is the wordplay.
'since' becomes 'as' (I've seen this in other clues).
'inferior' becomes 'under' (I've seen this in another clue).
'as'+'under'='ASUNDER'
(Other definitions for asunder that I've seen before include "being in two" , "separately" , "going to pieces" , "(Split) apart" , "Let no man put -" .)