Crossword Genius

Is jazz band mostly rubbish in engagement upset? (14)

Ross

I believe the answer is:

discombobulate

I'm a little stuck... Click here to teach me more about this clue!

'upset?' is the definition.
(discombobulating is a kind of upseting)

'is jazz band mostly rubbish in engagement' is the wordplay.
I cannot quite understand how this works, but
'is' is present in the answer.
'band' could be 'o' (I've seen this in other clues) and 'o' is located in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for discombobulate that I've seen before include "Confuse" , "Upset" , "cause confusion" , "Throw" , "rattle?" .)

I've seen this clue in The Times.
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