Vegetable piece split (9)
I believe the answer is:
mangetout
'vegetable' is the definition.
(I've seen this before)
'piece split' is the wordplay.
'piece' becomes 'man' (man can mean a chess piece).
'split' becomes 'get out' (in sense of leaving).
'man'+'getout'='MANGETOUT'
(Other definitions for mangetout that I've seen before include "From this pod" , "vegetables" , "Sugar peas" , "Vegetable" , "Type of pea" .)