Not for advantage in a way (7)
I believe the answer is:
against
'not for' is the definition.
(I've seen this before)
'advantage in a way' is the wordplay.
'advantage in' becomes 'again' (I can't justify this - if you can you should believe this answer much more).
'a way' becomes 'st' (abbreviation for street).
'again'+'st'='AGAINST'
Can you help me to learn more?
(Other definitions for against that I've seen before include "In conflict with" , "Opposing" , "Abutting" , "Facing" , "In opposition to" .)