Actors who no longer star, possibly? (6)
I believe the answer is:
extras
'actors' is the definition.
(extra is a kind of actor)
'no longer star possibly?' is the wordplay.
'no longer' becomes 'ex' (prefix meaning former or onetime).
'possibly?' indicates anagramming the letters (I've seen 'possibly' mean this).
'star' anagrammed gives 'tras'.
'ex'+'tras'='EXTRAS'
'who' is the link.
(Other definitions for extras that I've seen before include "5 [BYE BYE]" , "Bit actors in film" , "Spear-carriers" , "walk-on parts" , "Minor film actors" .)