Hairstyle that is a hit (4)
I believe the answer is:
bang
This clue is a double definition.
'hairstyle' is the first definition.
(bang is a kind of hairstyle)
'a hit' is the second definition.
('bang' can be a synonym of 'hit')
'that is' acts as a link.
(Other definitions for bang that I've seen before include "Sudden impact" , "Sound of explosion" , "Strike violently" , "Sudden loud noise (often 'big')" , "hit" .)