Comeback of Friends is a hit (4)
I believe the answer is:
slap
'a hit' is the definition.
(both can mean to strike)
'comeback of friends' is the wordplay.
'comeback of' is a reversal indicator.
'friends' becomes 'pals' (pal is a kind of friend).
'pals' written backwards gives 'SLAP'.
'is' is the link.
(Other definitions for slap that I've seen before include "Cuff" , "Hit with a flat hand" , "Hit with the palm" , "Strike with the palm" , "A blow among pals" .)