Walked out after initial clash and split (5)
I believe the answer is:
cleft
'split' is the definition.
(cleft can mean split or cloven)
'walked out after initial clash' is the wordplay.
'walked out' becomes 'left' (I've seen this in another clue).
'after' says to put letters next to each other.
'initial' says to take the initial letters.
The initial letter of 'clash' is 'c'.
'left' put after 'c' is 'CLEFT'.
'and' acts as a link.
(Other definitions for cleft that I've seen before include "Partially divided" , "Split or indentation" , "Split; fissure" , "split along natural lines" , "Space" .)