Fine about sponging rag on a knitted jumper (8)

I believe the answer is:

kangaroo

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'jumper' is the definition.
(I've seen this before)

I don't understand how the rest of the clue works.

(Other definitions for kangaroo that I've seen before include "Bounding marsupial" , "Marsupial that boxes" , "Illegal court of marsupial origin?" , "impromptu kind of court" , "Hopping marsupial" .)

I've seen this clue in The Hindu.

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