Forms groups of actors (5)
I believe the answer is:
casts
This clue is a double definition.
'forms' is the first definition.
(I know this)
'groups of actors' is the second definition.
(I've seen this before)
(Other definitions for casts that I've seen before include "Assigns an actor to a role" , "Eg puts" , "groups of actors" , "Allocates parts" , "Throws" .)