Friends come back for smack (4)
I believe the answer is:
slap
'for smack' is the definition.
(synonyms)
'friends come back' is the wordplay.
'friends' becomes 'pals' (pal is a kind of friend).
'come back' is a reversal indicator.
'pals' written backwards gives 'SLAP'.
(Other definitions for slap that I've seen before include "Blow, maybe in the face" , "Hit with an open hand" , "Hit with the palm" , "A blow among pals" , "Strike action" .)