Against a concession for homeless person (7)
I believe the answer is:
vagrant
'homeless person' is the definition.
(I've seen this before)
'against a concession' is the wordplay.
'against' becomes 'v' (abbreviation for 'versus').
'concession' becomes 'grant' ('grant' can be a synonym of 'concession').
'v'+'a'+'grant'='VAGRANT'
'for' is the link.
(Other definitions for vagrant that I've seen before include "Homeless wanderer" , "Homeless person" , "Wandering tramp" , "Itinerant" , "Traveller" .)