Hard knocks? (4)
(Other definitions for raps that I've seen before include "Sprechgesang pop hits" , "Knocks sharply" , "'Knocks, on the door say (4)'" , "Cracks" .)
'hard knocks' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for bops that I've seen before include "hits" , "Dances to pop" .)