Jumper over the moon? (6,3)

I believe the answer is:

jersey cow

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'moon?' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'jumper over' is the wordplay.
'jumper' becomes 'jersey' (I've seen this before).
'over' becomes 'cow' (I can't explain this - if you can you should give a lot more credence to this answer).
'jersey'+'cow'='JERSEY COW'

'the' is the link.

Can you help me to learn more?

I've seen this clue in The Telegraph.

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