The most common and most likely answer to this crossword clue is the 5 letter word FETID
I've seen this crossword clue in Financial Times
F
E
T
I
D
More clues leading to the result FETID
- Stinking US agent pulling in upset relations
- Rank claimed by guard — it effectively rises
- Foul in football? Expect trouble in derby, all kicking off
- This regularly cuts Iron Duke’s rank
- Rank of American agent taking on Tori’s case
- Satisfied around half-time or raising a stink?
- Fellow’s tied in knots, getting high
- Rank of US lawman apprehending part timer.
- Fine time to promote energy, making a stink
Buddy explains!

The straight part
We know that "Foul" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case foul = fetid.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 FETID mean?
FETID noun- The foul-smelling asafoetida plant, or its extracts.
- Foul-smelling, stinking.