The most common and most likely answer to this crossword clue is the 6 letter word RESIGN
I've seen this crossword clue in The Times
R
E
S
I
G
N
More clues leading to the result RESIGN
- Concerned with omen, stand down
- Give up working rule to accommodate first of students
- Breaking rule, son gets to step down
- Quit securing entrance to garden with gum
- Give up tenure or commit oneself again?
- Give up job as lousy singer
- Plan with right for Democrat to step aside
- Rule restricting soldier’s first leave
- Rule over Sweden then quit
- Extend contract or quit
Buddy explains!

The straight part
We know that "stand down" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case stand down = resign.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 RESIGN mean?
RESIGN verb- To give up; to relinquish ownership of.
- To hand over (something to someone), place into the care or control of another.
- To quit (a job or position).
- To submit passively; to give up as hopeless or inevitable.
- To sign again; to provide one's signature again.
- (by extension) To sign a contract renewing or restarting a professional relationship, such as that of a professional athlete with a sports team.