Attack in the ring? (5,2)

I believe the answer is:
round on
'attack' is the definition.
('round on' can be a synonym of 'attack')
'ring?' is the wordplay.
I cannot quite see how this works, but
'ring?' could be 'round' ('round' can be a synonym of 'ring') and 'round' 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 clue (or it may be nonsense).
'in the' is the link.
Can you help me to learn more?
(Other definitions for round on that I've seen before include "Attack verbally" , "Suddenly attack (someone)" , "Make unexpected retort of circular kind" , "Retort in retaliation, perhaps unexpectedly (5,2)" .)
