The most common and most likely answer to this crossword clue is the 9 letter word SHABBIEST
I've seen this crossword clue in Financial Times
S
H
A
B
B
I
E
S
T
Buddy explains!

The straight part
We know that "Extremely scruffy" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case extremely scruffy = shabbiest.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 SHABBIEST mean?
SHABBIEST adjective- Torn or worn; unkempt.
- Clothed with ragged, much worn, or soiled garments.
- Mean; paltry; despicable.