The most common and most likely answer to this crossword clue is the 8 letter word DISMOUNT
I've seen this crossword clue in The Daily Telegraph
D
I
S
M
O
U
N
T
Buddy explains!

The straight part
We know that "Get off" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case get off = dismount.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 DISMOUNT mean?
DISMOUNT noun- The part of a routine in which the gymnast detaches from an apparatus.
- To (cause to) get off (something).
- To make (a mounted drive) unavailable for use.
- To come down; to descend.
- To throw (cannon) off their carriages.