Stage direction stops working in theatre play (3,11)
I believe the answer is:
the entertainer
'play' is the definition.
(1957 play by John Osborne)
'stage direction stops working in theatre' is the wordplay.
'stage direction' becomes 'enter' (stage direction to take to the stage).
'stops' is an insertion indicator.
'working' indicates anagramming the letters.
'in'+'theatre'='intheatre'
'intheatre' with letters rearranged gives 'thetainer'.
'enter' going within 'thetainer' is 'THE ENTERTAINER'.
(Other definitions for the entertainer that I've seen before include "a ragtime piece" , "Osborne play" , "Piano rag by Scott Joplin" .)