Box up hip-hop performances (4)
I believe the answer is:
raps
'hip-hop performances' is the definition.
(rap is used in hip-hop)
'box up' is the wordplay.
'box' becomes 'spar' (spar can mean to box).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'spar' backwards is 'RAPS'.
(Other definitions for raps that I've seen before include "Knocks sharply" , "Cracks" , "Sprechgesang pop hits" , "'Knocks, on the door say (4)'" .)