His map is incorrect, causing an accident (6)
I believe the answer is:
mishap
'an accident' is the definition.
(mishap is a kind of accident)
'his map is incorrect' is the wordplay.
'is incorrect' is an anagram indicator.
'his'+'map'='hismap'
'hismap' with letters rearranged gives 'MISHAP'.
'causing' is the link.
(Other definitions for mishap that I've seen before include "An accident or unlucky event" , "Stroke of bad luck" , "'Bad luck, mischance (6)'" , "Contretemps" , "Unfortunate minor accident" .)