Smash duo nearly producing song (9)
I believe the answer is:
roundelay
'song' is the definition.
(roundelay is a kind of song)
'smash duo nearly' is the wordplay.
'smash' is an anagram indicator.
'duo'+'nearly'='duonearly'
'duonearly' with letters rearranged gives 'ROUNDELAY'.
'producing' is the link.
(Other definitions for roundelay that I've seen before include "Slow dance - song with refrain" , "Short, simple song" , "Circle dance; simple song" , "Slow, circling medieval dance" , "Slow, medieval dance, in a circle" .)