Watched part of play broadcast (4)
I believe the answer is:
seen
'watched' is the definition.
(I've seen this before)
'part of play broadcast' is the wordplay.
'part of play' becomes 'scene' ('scene' is part of 'play').
'broadcast' indicates a 'sounds like' (homophone) clue (how the word might sound on the radio or TV).
'scene' sounds like 'SEEN'.
(Other definitions for seen that I've seen before include "Perceived by sight" , "Spotted" , "watched" , "Espied" , "Sighted" .)