Things used to assault son during attacks (5)
I believe the answer is:
fists
'things used to assault' is the definition.
'son during attacks' is the wordplay.
'son' becomes 's'.
'during' is an insertion indicator.
'attacks' becomes 'fits' (fit is a kind of attack**).
's' going into 'fits' is 'FISTS'.
(Other definitions for fists that I've seen before include "Doubled up hands" , "Boxer's punchers" , "Dukes" , "Fighting tools" , "bunches of five" .)