Ostracise NCO, voted out after cutting guard (4,2,8)
I believe the answer is:
send to coventry
'ostracise' is the definition.
(thesaurus)
'nco voted out after cutting guard' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'after cutting' indicates putting letters inside.
'guard' becomes 'sentry' (sentry is a kind of guard**).
'nco'+'voted'='ncovoted'
'ncovoted' is an anagram of 'dtocoven'.
'dtocoven' inserted within 'sentry' is 'SEND TO COVENTRY'.
(Other definitions for send to coventry that I've seen before include "exclude" , "Ignore" , "Ostracise" , "blank" .)