Unhappy on stage, so quit (4,4)
I believe the answer is:
step down
'quit' is the definition.
('step down' can be a synonym of 'quit')
'unhappy on stage' is the wordplay.
'unhappy' becomes 'down' (I've seen this before).
'on' is a charade indicator (letters next to each other).
'stage' becomes 'step' (I've seen this before).
'down' after 'step' is 'STEP-DOWN'.
'so' is the link.
(Other definitions for step down that I've seen before include "Withdraw from" , "Gradually reduce - resign" , "Give up office" , "Resign, retire" , "Get off one's soap-box" .)