Hits with small underwear (5)
I believe the answer is:
socks
'hits' is the definition.
(socking is a kind of hitting)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for socks that I've seen before include "Foot covers" , "Disappointment at Xmas" , "pair of garments" , "Short stockings" , "Footwear - strikes" .)