Faulty legal process, one I abandoned —a big blow (7)
I believe the answer is:
mistral
'big blow' is the definition.
(strong wind)
I cannot understand how the rest of the clue works.
(Other definitions for mistral that I've seen before include "Strong north wind of southern France" , "Strong cold dry wind" , "A harsh blow" , "Violent northeast wind of southern France" , "Cold dry wind in southern France" .)