The most common and most likely answer to this crossword clue is the 7 letter word JACKASS
I've seen this crossword clue in Financial Times
J
A
C
K
A
S
S
More clues leading to the result JACKASS
Buddy explains!

The straight part
We know that "Fool" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fool = jackass.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 JACKASS mean?
JACKASS noun- A male donkey
- A foolish or stupid person
- An inappropriately rude or obnoxious person
- To behave very obnoxiously
- A jack and an ace as a starting hand in Texas hold 'em due to phonetic similarity