Stage left, for instance (3)
I believe the answer is:
leg
'stage' is the definition.
('leg' can be a synonym of 'stage')
'left for instance' is the wordplay.
'left' becomes 'l' (common abbreviation).
'for instance' becomes 'eg' ('e.g.' can be a synonym of 'for instance'**).
'l'+'eg'='LEG'
(Other definitions for leg that I've seen before include "Member" , "Poultry portion" , "part of course" , "Gigot" , "Support; cricket side" .)