Sacked very old supporting artist (7)
I believe the answer is:
ravaged
'sacked' is the definition.
('ravaged' can be a synonym of 'sacked')
'very old supporting artist' is the wordplay.
'very' becomes 'v' (abbreviation).
'old' becomes 'aged' ('aged' can be similar in meaning to 'old'**).
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'artist' becomes 'ra' (Royal Academician, member of Royal Academy of Arts).
'v'+'aged'='vaged'
'vaged' after 'ra' is 'RAVAGED'.
(Other definitions for ravaged that I've seen before include "Despoiled and pillaged" , "Devastated, having suffered great damage" , "laid waste" , "with wrecked appearance" .)