Unkempt sort in XS jumper given sack (7)

I believe the answer is:

fleabag

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'unkempt sort in xs' is the definition.
I can't judge whether this definition defines the answer.

'jumper given sack' is the wordplay.
'jumper' becomes 'flea' (something that jumps).
'given' means one lot of letters go next to another.
'sack' becomes 'bag' (I've seen this in another clue).
'flea'+'bag'='FLEABAG'

Can you help me to learn more?

(Other definitions for fleabag that I've seen before include "run-down hotel" , "Dirty person or animal" , "Scruffy person; seedy hotel (US)" , "Scruffy animal" .)

I've seen this clue in The Sunday Times and The Times.

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