Open-handed hit (4)
I believe the answer is:
slap
'open-handed hit' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for slap that I've seen before include "Strike action" , "Strike with the palm" , "Make-up (slang)" , "Blow (in face, on back, wrist)" , "Blow with open hand" .)