The most common and most likely answer to this crossword clue is the 8 letter word CLEAVERS
I've seen this crossword clue in The Times
C
L
E
A
V
E
R
S
More clues leading to the result CLEAVERS
Buddy explains!
The straight part
We know that "They could hack off" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they could hack off = cleavers.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 CLEAVERS mean?
CLEAVERS noun- A squarish, heavy knife used by butchers for hacking through bones, etc.
- (Bahamas) A type of clave, or rhythm stick, a concussive musical instrument used in traditional Bahamian music.
- (metaphoric) The act of eliminating someone or something, especially when done by someone with a history of other eliminations; a dismissal, rejection, or removal.
- Galium aparine, a herbaceous annual plant of the family Rubiaceae.