Regarded as part of the play, say (4)
I believe the answer is:
'regarded' is the definition.
'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' is a homophone of '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" .)