Mad about the knockout (4)
I believe the answer is:
stun
'mad about' is the definition.
('nuts' backwards)
'the knockout' is the wordplay.
I cannot quite understand how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is located in the answer.
The remaining letters 'sun' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for stun that I've seen before include "deliver a knock-out blow" , "'Shock, daze (4)'" , "Astound; render senseless" , "Knock out temporarily" , "Knock unconscious" .)