A stunning performance in The Ring? (4)
I believe the answer is:
kayo
'a stunning' is the definition.
I can't judge whether this defines the answer.
'performance in the ring?' is the wordplay.
'performance in' becomes 'kay' (I can't justify this - if you can you should give a lot more credence to this answer).
'the ring?' becomes 'o' (letter resembling a ring).
'kay'+'o'='KAYO'
Can you help me to learn more?
(Other definitions for kayo that I've seen before include "floor" , "Knock out in boxing" , "Stun" , "Decisive blow (in boxing)" , "Conclusive end of a boxing match" .)