Viewers in theatre yesterday (4)
I believe the answer is:
eyes
'viewers' is the definition.
(I've seen this in another clue)
'in theatre yesterday' is the wordplay.
'in' says the answer is hidden in the clue.
'EYES' is hidden in the letters of 'theatre yesterday'.
(Other definitions for eyes that I've seen before include "Looks at carefully" , "(Paradoxical?) film with Cruise and Kidman" , "Peacock's tail markings" , "Views" , "They look" .)