Open-handed blow (4)
'open-handed blow' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for slap that I've seen before include "Sharp smack" , "Blow (in face, on back, wrist)" , "Right" , "Hit with the palm" , "Hit with an open hand" .)
(Other definitions for cuff that I've seen before include "End of arm" , "minor assault" , "beat" , "Strike" , "Part of garment covering wrist" .)