Remove actor in crowd scene to join depleted cast (7)
I believe the answer is:
extract
'remove' is the definition.
(thesaurus)
'actor in crowd scene to join depleted cast' is the wordplay.
'actor in crowd scene' becomes 'extra'.
'to join' is a charade indicator (letters next to each other).
'depleted' means to remove the middle letters.
'cast' with its centre removed is 'ct'.
'extra'+'ct'='EXTRACT'
(Other definitions for extract that I've seen before include "Find out" , "quarry" , "Remove by force" , "bit" , "essence" .)