The most common and most likely answer to this crossword clue is the 9 letter word SELF-HARM
I've seen this crossword clue in The Guardian
S
E
L
F
-
H
A
R
M
Buddy explains!

The straight part
We know that "Damage flesh with knife?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case damage flesh with knife? = self-harm.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 SELF-HARM mean?
SELF-HARM noun- The deliberate non-suicidal injuring of one's own body.
- To harm oneself deliberately.