Observed and listened to part of play (4)
I believe the answer is:
seen
'observed' is the definition.
('seen' can be a synonym of 'observed')
'listened to part of play' is the wordplay.
'listened to' shows a homophone (sound like).
'part of play' becomes 'scene' ('scene' is part of 'play').
'scene' sounds like 'SEEN'.
'and' is the link.
(Other definitions for seen that I've seen before include "Witnessed" , "Espied" , "Viewed" , "watched" , "Perceived by sight" .)