The most common and most likely answer to this crossword clue is the 6 letter word SEETHE
I've seen this crossword clue in Financial Times
S
E
E
T
H
E
More clues leading to the result SEETHE
Buddy explains!
The straight part
We know that "foam at the mouth" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case foam at the mouth = seethe.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 SEETHE mean?
SEETHE verb- To boil.
- (of a liquid) To boil vigorously.
- (of a liquid) To foam in an agitated manner, as if boiling.
- (of a person) To be in an agitated or angry mental state, as if boiling.
- (of a place) To buzz with activity.