Pity actor entering empty stage (5)
I believe the answer is:
shame
'pity' is the definition.
(I know that pity can be written as shame)
'actor entering empty stage' is the wordplay.
'actor' becomes 'ham' (ham is a kind of actor).
'entering' is an insertion indicator.
'empty' suggests removing the centre.
'stage' with its middle removed is 'se'.
'ham' going within 'se' is 'SHAME'.
(Other definitions for shame that I've seen before include "Ignomony" , "Painful emotion resulting from guilt" , "scandal" , "show up" , "Disgrace - Salman Rushdie novel" .)