Among guilty parties losing appeal with irritated snarl (10)
I believe the answer is:
complicate
'snarl' is the definition.
(thesaurus)
'among guilty parties losing appeal with irritated' is the wordplay.
'among guilty parties' becomes 'complicit' (eg complicit in a crime).
'losing' indicates named letters should be taken away.
'appeal' becomes 'it' ('it' can mean something attractive or appealing).
'with' says to put letters next to each other.
'irritated' becomes 'ate' (something eating at something is irritating them).
'complicit' with 'it' taken away is 'complic'.
'complic'+'ate'='COMPLICATE'
(Other definitions for complicate that I've seen before include "Make less simple" , "Make involved" , "Make intricate" , "muddle" .)