The most common and most likely answer to this crossword clue is the 10 plus 5 letter word INCIDENTAL MUSIC
I've seen this crossword clue in Financial Times
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More clues leading to the result INCIDENTAL MUSIC
- Mini-acts include fanciful pieces for the pit orchestra maybe
- Score during period of play
- At home playing Celtic, Man U side almost score
- Bars not essential in the theatre?
- Part of film maybe naturally attached to rock?
- Background notes including medical units rewritten
- Striking folk, for example, that may be arranged to back up action
- It’s not essential entertainment
- … and slim in cute pants, in charge for film soundtrack, maybe
- What allows some air into a dramatic stand-off?
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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.