The most common and most likely answer to this crossword clue is the 9 letter word ABANDONED
I've seen this crossword clue in The Times
A
B
A
N
D
O
N
E
D
More clues leading to the result ABANDONED
- Uninhibited group one's seen in a day
- Finished feeding a group left behind
- Ban on dead bats is crazy
- Resigned from music group, one featuring in commercial
- A bit of kebab and one doughnut left
- A group on ecstasy and speed, ultimately very wild
- Wild graduate upset with single daughter
- Possibly sleeping around with old knight is wild
- A forbidden drinking party? Crazy!
- . Wild party held in a bar by Scottish delinquent
Buddy explains!

The straight part
We know that "left behind" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case left behind = abandoned.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 ABANDONED mean?
ABANDONED verb- To give up or relinquish control of, to surrender or to give oneself over, or to yield to one's emotions.
- To desist in doing, practicing, following, holding, or adhering to; to turn away from; to permit to lapse; to renounce; to discontinue.
- To leave behind; to desert as in a ship or a position, typically in response to overwhelming odds or impending dangers; to forsake, in spite of a duty or responsibility.
- To subdue; to take control of.
- To cast out; to banish; to expel; to reject.
- To no longer exercise a right, title, or interest, especially with no interest of reclaiming it again; to yield; to relinquish.
- To surrender to the insurer (an insured item), so as to claim a total loss.
- Having given oneself up to vice; immoral; extremely wicked, or sinning without restraint; irreclaimably wicked.
- No longer maintained by its former owners, residents or caretakers; forsaken, deserted.
- Free from constraint; uninhibited.
- No longer being acted upon by the geologic forces that formed it.