Accident sort of interrupts plan (6)
I believe the answer is:
mishap
'accident' is the definition.
(I know that accident can be written as mishap)
'sort of interrupts plan' is the wordplay.
'sort of' becomes 'ish' (I've seen this in other clues).
'interrupts' is an insertion indicator.
'plan' becomes 'map' (plan can mean a map of something).
'ish' put inside 'map' is 'MISHAP'.
(Other definitions for mishap that I've seen before include "Unfortunate occurrence" , "'Accident, bad luck (6)'" , "Unpleasant accident" , "An accident, piece of bad luck" , "Unfortunate minor accident" .)