Regarded as part of the play, say (4)
I believe the answer is:
seen
'regarded' is the definition.
(I've seen this in another clue)
'part of the play say' is the wordplay.
'part of the play' becomes 'scene' ('scene' is part of 'play').
'say' shows a homophone (sound like).
'scene' sounds like 'SEEN'.
'as' acts as a link.
(Other definitions for seen that I've seen before include "Witnessed" , "Noticed" , "Perceived by sight" , "Sighted" , "Observed or percieved" .)