Scrap lorry that doesn't start (4)
I believe the answer is:
ruck
'scrap' is the definition.
(both can mean a fight)
'lorry that doesn't start' is the wordplay.
'lorry' becomes 'truck' (I've seen this before).
'that doesn't start' means to remove the first letter.
'truck' with its initial letter removed is 'RUCK'.
(Other definitions for ruck that I've seen before include "Undistinguished crowd - irregular crease" , "Fight" , "Loose scrummage" , "Cower" , "Indistinguishable heap - a loose 10" .)