Rabble repeated phrase by gunmen very loudly (8)
I believe the answer is:
riffraff
'rabble' is the definition.
(I know that rabble can be written as riffraff)
'repeated phrase by gunmen very loudly' is the wordplay.
'repeated phrase' becomes 'riff' (I've seen this in another clue).
'by' says to put letters next to each other.
'gunmen' becomes 'RA' (abbreviation for Royal Artillery).
'very loudly' becomes 'ff' (short for fortissimo, 'very loud' in music).
'riff'+'ra'+'ff'='RIFFRAFF'
(Other definitions for riffraff that I've seen before include "Dregs of society" , "Undesirables" , "Crowd regarded with disdain" , "Hoi polloi" , "Disreputable people, rabble" .)