Beats half of them and steals from (6)
I believe the answer is:
throbs
'beats' is the definition.
(I know this)
'half of them and steals from' is the wordplay.
'half of' suggests halving the letters.
'and' says to put letters next to each other.
'steals from' becomes 'robs' (I've seen this before).
'them' cut in half is 'th'.
'th'+'robs'='THROBS'
(Other definitions for throbs that I've seen before include "Beats with persistent rhythm, as heart does" , "Beats as a pulse" , "Pulsates like heart" , "Pounds" , "Pulsates, with pain perhaps" .)