The most common and most likely answer to this crossword clue is the 9 letter word PROMISING
P
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Buddy explains!

The straight part
We know that "Up-and-coming" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case up-and-coming = promising.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 PROMISING mean?
PROMISING verb- To commit to (some action or outcome), or to assure (a person) of such commitment; to make an oath or vow.
- To give grounds for expectation, especially of something good.
- The act of making a promise.
- Showing promise, and likely to develop in a desirable fashion.
- Encouraging and inspiring confidence.