Make light of losing on stage show (4,4)
I believe the answer is:
play down
'make light of' is the definition.
(I've seen this before)
'losing on stage show' is the wordplay.
'losing' becomes 'down' ('down' can be similar in meaning to 'losing').
'on' means one lot of letters go next to another.
'stage show' becomes 'play'.
'down' put after 'play' is 'PLAY DOWN'.
(Other definitions for play down that I've seen before include "what Antrim team may do?" , "Gloss over" , "Minimise the importance of (something)" , "Give little importance to" , "Make light of" .)