Decisive defeat in ring — count out (9)
I believe the answer is:
trouncing
'decisive defeat' is the definition.
(I've seen this in another clue)
'ring count out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'ring'+'count'='ringcount'
'ringcount' is an anagram of 'TROUNCING'.
'in' is the link.
(Other definitions for trouncing that I've seen before include "Heavily defeating" , "Beating" .)