Nice knockback either way (3)
I believe the answer is:
non
'nice' is the definition.
Both the answer and definition are adjectives. Perhaps you can see an association between them that I can't see?
'knockback either way' is the wordplay.
I cannot really see how this works, but
'way' could be 'n' (Compass direction - North) and 'n' is located in the answer.
The remaining letters 'on' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for non that I've seen before include "Prefixed negation of a word" , "Negative French word" , "- - -stick" , "Prefix meaning not or none" , "Combining form meaning not" .)