Refuse to acknowledge down is out (6)
I believe the answer is:
disown
'refuse to acknowledge' is the definition.
(I've seen this before)
'down is out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'down'+'is'='downis'
'downis' is an anagram of 'DISOWN'.
(Other definitions for disown that I've seen before include "Reject all connection or relationship with" , "Disclaim or deny" , "Refuse to be connected with" , "Cast aside" , "Deny any connection with" .)