The most common and most likely answer to this crossword clue is the 9 letter word SHARPNESS
I've seen this crossword clue in The Times
S
H
A
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P
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Buddy explains!
The straight part
We know that "Perspicacity/unwelcome in performing musicians?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case perspicacity/unwelcome in performing musicians? = sharpness.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 SHARPNESS mean?
SHARPNESS noun- The cutting ability of an edge; keenness
- The fineness of the point a pointed object
- The product or result of being sharp.
- (of food etc) pungency or acidity
- (of an image) distinctness, focus
- (of intelligence) acuteness or acuity
- Edge or blade