The most common and most likely answer to this crossword clue is the 8 letter word DITCHING
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Buddy explains!

The straight part
We know that "Leaving" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case leaving = ditching.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 DITCHING mean?
DITCHING verb- To smear, daub, plaster, or impregnate, especially with dirt which becomes hard and ingrained.
- To discard or abandon.
- To deliberately crash-land an airplane on water.
- To deliberately not attend classes; to play hookey.
- To dig ditches.
- To dig ditches around.
- To throw into a ditch.
- A deliberate crash landing on the sea.