Fight taking one second, on average (4)
I believe the answer is:
spar
'fight' is the definition.
(sparring is a kind of fighting)
'one second on average' is the wordplay.
'one second' becomes 's' (common abbreviation).
'on' is a charade indicator (letters next to each other).
'average' becomes 'par' (I've seen this before).
's'+'par'='SPAR'
'taking' is the link.
(Other definitions for spar that I've seen before include "Fight - something probably rigged?" , "Crystal - box" , "Sticks" , "supporting member" , "Argue" .)