Actors in some of America's theatres (4)
I believe the answer is:
cast
'actors' is the definition.
(group of actors)
'some of america's theatres' is the wordplay.
'some of' indicates the answer is hidden within the clue.
'CAST' is hidden within 'americas theatres'.
'in' is the link.
(Other definitions for cast that I've seen before include "Throw out line for fish" , "The acting complement of a play" , "Troupe" , "Throw a fishing line" , "Mould; actors in a play" .)