Outdoor writer bursting into love song (4-3)
I believe the answer is:
open-air
'outdoor' is the definition.
(outdoor means out in the open air)
'writer bursting into love song' is the wordplay.
I cannot really understand how this works, but
'writer' could be 'pen' (something which writes) and 'pen' is found in the answer.
'love' could be 'o' (love means zero in tennis) and 'o' is found in the answer.
'song' could be 'air' (I've seen this before) and 'air' is found in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for open-air that I've seen before include "outside" , "Exposed to the elements" , "Alfresco" , "Taking place outdoors" , "Outdoor" .)