The most common and most likely answer to this crossword clue is the 9 letter word BACKSLASH
I've seen this crossword clue in Financial Times
B
A
C
K
S
L
A
S
H
More clues leading to the result BACKSLASH
- Angry reaction engulfing small character
- Left-leaning character is in favour of corporal punishment
- One leaning to the left supports strike
- Negative reaction about small mark
- Character inclined to support strike involving cuts
- Mark supports strike
- Regressive character favours corporal punishment
- Support cut symbolically?
- Reverend’s loose party character
- Mark a clue that does this for golf
Buddy explains!

The straight part
We know that "One leaning to the left" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one leaning to the left = backslash.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 BACKSLASH mean?
BACKSLASH noun- The punctuation mark \.
- Used erroneously in reference to, or in reading out, the ordinary slash, that is, the punctuation mark /.
- To escape (a metacharacter) by prepending a backslash that serves as an escape character, thereby forming an escape sequence.