Hit a second time, knocking out (5)
I believe the answer is:
smite
'hit' is the definition.
(smiting is a kind of hitting)
'a second time knocking out' is the wordplay.
'a second' becomes 's' (common abbreviation**).
'knocking' indicates anagramming the letters.
'out' is an insertion indicator.
'time' is an anagram of 'mite'.
's' put within 'mite' is 'SMITE'.
(Other definitions for smite that I've seen before include "Thwack" , "Beat" , "Funeral pile" , "Strike with a firm blow" , "Strike firmly" .)