Start song outside (4-3)
I believe the answer is:
open-air
'outside' is the definition.
('open-air' can be similar in meaning to 'outside')
'start song' is the wordplay.
'start' becomes 'open' (opening is a kind of starting).
'song' becomes 'air' (I've seen this before).
'open'+'air'='OPEN-AIR'
(Other definitions for open-air that I've seen before include "Exposed to the elements" , "Outdoor" , "outside" , "Taking place outdoors" , "Alfresco" .)