Under Control' playing (a bit of a racket) (2,1,6)
I believe the answer is:
on a string
'under control'' is the definition.
(I've seen this before)
'playing a bit of a racket' is the wordplay.
'playing' becomes 'on' (on can mean playing or performing).
'bit of a racket' becomes 'string' (I can't explain this - if you can you should give a lot more credence to this answer).
'on'+'a'+'string'='ON A STRING'
Can you help me to learn more?
(Other definitions for on a string that I've seen before include "under one's control" , "Pearl may be" , "under complete control" , "left dangling?" , "Yo-yo is" .)