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