Reportedly, brown square finished (4,3)
I believe the answer is:
done for
'finished' is the definition.
(synonyms)
'reportedly brown square' is the wordplay.
'reportedly' indicates a 'sounds like' (homophone) clue.
'brown' becomes 'dun' (dun is a kind of brown).
'square' becomes 'for' (I can't justify this - if you can you should give a lot more credence to this answer).
'dun' is a homophone of 'done'.
'done'+'for'='DONE FOR'
(Other definitions for done for that I've seen before include "Ruined" , "in serious trouble" , "killed" , "condemned" , "close to death" .)