The most common and most likely answer to this crossword clue is the 6 letter word RECUSE
I've seen this crossword clue in The Guardian
R
E
C
U
S
E
Buddy explains!

The straight part
We know that "Announce as unsuitable" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case announce as unsuitable = recuse.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does RECUSE mean?
RECUSE verb- To refuse or reject (a judge); to declare that the judge shall not try the case or is disqualified from acting.
- (of a judge) To refuse to act as a judge; to declare oneself disqualified from acting.