Smack, or beat with force pressing down (4)
I believe the answer is:
tang
'smack' is the definition.
('tang' can be a synonym of 'smack')
'beat with force pressing down' is the wordplay.
'beat' becomes 'tan' (I've seen this before).
'with' is a charade indicator (letters next to each other).
'force pressing down' becomes 'g' (abbreviation for gravity as in G-force).
'tan'+'g'='TANG'
'or' is the link.
(Other definitions for tang that I've seen before include "Beat, with good" , "Aroma" , "Savour" , "Gnat (anag.)" , "characteristic quality" .)