Criminal eating a soft fattened fowl (5)
I believe the answer is:
capon
'fattened fowl' is the definition.
'criminal eating a soft' is the wordplay.
'criminal' becomes 'con' (abbreviation for 'convict').
'eating' indicates putting letters inside.
'soft' becomes 'p' (musical abbreviation for 'piano').
'a'+'p'='ap'
'con' placed around 'ap' is 'CAPON'.
(Other definitions for capon that I've seen before include "Castrated bird" , "fowl fattened for pot" , "Male fowl fattened for eating" , "Castrated cock fowl" , "for lunch, perhaps" .)