Cheap newspaper has a stock phrase for the riff-raff (6)
I believe the answer is:
ragtag
'the riff-raff' is the definition.
(I've seen this before)
'cheap newspaper has a stock phrase' is the wordplay.
'cheap newspaper' becomes 'rag' (rag can mean a low-quality newspaper).
'has' says to put letters next to each other.
'a stock phrase' becomes 'tag'.
'rag'+'tag'='RAGTAG'
'for' acts as a link.
(Other definitions for ragtag that I've seen before include "Badly organised" , ". . . . . . and bobtail, the rabble" , "Common people, riff-raff - ...... and bobtail" , "Scruffy" , "Incongruously varied in character" .)