Go down with a bristle (4)
I believe the answer is:
seta
'bristle' is the definition.
(I've seen this before)
'go down with a' is the wordplay.
'go down' becomes 'set' (setting is a kind of going down).
'with' is a charade indicator (letters next to each other).
'set'+'a'='SETA'
(Other definitions for seta that I've seen before include "bristle" , "bristle-like appendage" , "Criminals make the best detectives" .)