Pole blows up (4)
I believe the answer is:
spar
'pole' is the definition.
(I know that spar is a type of pole)
'blows up' is the wordplay.
'blows' becomes 'raps' (rap is a kind of blow).
'up' is a reversal indicator (in down clue: letters go upwards).
'raps' reversed gives 'SPAR'.
(Other definitions for spar that I've seen before include "Practise boxing with a pole?" , "bar" , "Raps with strong pole" , "quarrel" , "Pole used in boat etc - box" .)