In secret, nude knotted on chair with middle cut out around balls (10)
I believe the answer is:
undercover
'in secret' is the definition.
(thesaurus)
'cut out around balls' is the wordplay.
'cut out' becomes 'under' (I've seen this in another clue. I am not sure about the 'cut' bit.).
'around' becomes 'c' (abbreviation for 'circa').
'balls' becomes 'over' (I've seen this in other clues).
'under'+'c'+'over'='UNDERCOVER'
'nude knotted on chair with middle' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for undercover that I've seen before include "What spy may be" , "Clandestine" , "Hidden" , "Secret (operations)" , "Agent's description" .)