Grand group of swingers (3,4)
I believe the answer is:
big band
'swingers' is the definition.
(musicians who might play swing music)
'grand group' is the wordplay.
'grand' becomes 'big'.
'group' becomes 'band' (band can mean a group of people).
'big'+'band'='BIG BAND'
'of' acts as a link.
(Other definitions for big band that I've seen before include "Large jazz ensemble" , "Dance orchestra of 30s" , "Large group of musicians" .)