Go hunt, us? Quite otherwise, if something's this (8)
I believe the answer is:
unsought
'something's this' is the definition.
The definition suggests a singular noun but the answer is not.
'go hunt us? quite otherwise' is the wordplay.
'quite otherwise' is an anagram indicator.
'go'+'hunt'+'us'='gohuntus'
'gohuntus' anagrammed gives 'UNSOUGHT'.
'if' acts as a link.
(Other definitions for unsought that I've seen before include "Untried" , "not requested" , "unlike Sir Percy Blakeney" , "Not looked for or desired" .)