This jumper could really make you itch! (4)

I believe the answer is:

flea

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'this jumper' is the definition.
(something that jumps)

I cannot understand how the rest of the clue works.

(Other definitions for flea that I've seen before include "little pest" , "Wingless, jumping insect" , "Jumping, blood-sucking insect" , "source of infestation" , "Blood-sucking parasites" .)

I've seen this clue in The Guardian.

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