The most common and most likely answer to this crossword clue is the 4 letter word GOOF
I've seen this crossword clue in Financial Times
G
O
O
F
More clues leading to the result GOOF
- Blunder and nearly get fired
- Mistake to leave without finishing
- Mistake: err briefly
- Explode without full force? That’s a mistake
- Almost stop working, stupid
- Excessive sentimentality following mistake
- Work of genius this is not
- Fluff in endless decay
- Largely cease to be fond of stupid person
- Make a mistake and almost quit
Buddy explains!

The straight part
We know that "Mistake" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case mistake = goof.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 GOOF mean?
GOOF noun- A mistake or error.
- A foolish and/or silly person; a goofball.
- A child molester.
- To make a mistake.
- To engage in mischief.