Fine about sponging rag on a knitted jumper (8)
I believe the answer is:
kangaroo
'jumper' is the definition.
(I've seen this before)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(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" .)