Could start to whip in a fight (5)
I believe the answer is:
clash
'a fight' is the definition.
(clash is a kind of fight)
'could start to whip' is the wordplay.
'start to' says to take the initial letters.
'whip' becomes 'lash' (synonyms).
The initial letter of 'could' is 'c'.
'c'+'lash'='CLASH'
'in' acts as a link.
(Other definitions for clash that I've seen before include "jar" , "Punk group; disagree" , "Conflict, discord" , "(Of colours) look inappropriate together" , "Conflict, between colours say" .)