The most common and most likely answer to this crossword clue is the 11 letter word BLAMEWORTHY
I've seen this crossword clue in The Daily Telegraph
B
L
A
M
E
W
O
R
T
H
Y
More clues leading to the result BLAMEWORTHY
Buddy explains!

The straight part
We know that "Being at fault" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case being at fault = blameworthy.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 BLAMEWORTHY mean?
BLAMEWORTHY adjective- Deserving blame or censure; reprehensible.