Bit of bad luck (6)
I believe the answer is:
mishap
'bit of bad luck' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for mishap that I've seen before include "An accident, piece of bad luck" , "'Accident, bad luck (6)'" , "An accident or unlucky event" , "Blow" , "Unlucky development" .)