Knock pals around (4)
I believe the answer is:
slap
'knock' is the definition.
(thesaurus)
'pals around' is the wordplay.
'around' is a reversal indicator.
'pals' back-to-front is 'SLAP'.
(Other definitions for slap that I've seen before include "Blow, maybe in the face" , "Right" , "A blow among pals" , "Hit with an open hand" , "Mild punishment" .)