Obstruction is brief? No way (7)
I believe the answer is:
barrier
'obstruction' is the definition.
(I know that barrier is a type of obstruction)
'brief? no way' is the wordplay.
'brief?' becomes 'barrister' (brief can mean a lawyer).
'no' suggests deleting specific letters.
'way' becomes 'st' (abbreviation for street).
'barrister' with 'st' taken away is 'BARRIER'.
'is' acts as a link.
(Other definitions for barrier that I've seen before include "Impediment" , "Wall - fence" , "Structure preventing access" , "Stockade - obstacle" , "Fence; obstacle" .)