The most common and most likely answer to this crossword clue is the 6 letter word NUCHAL
N
U
C
H
A
L
Buddy explains!

The straight part
We know that "like a rabbit punch" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case like a rabbit punch = nuchal.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 NUCHAL mean?
NUCHAL noun- The back of the neck.
- Short for nuchal translucency scan.
- A neck scale, especially of a lizard.
- Of or pertaining to the back or nape of the neck.