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