Getting worse at skiing? (5,8)

I believe the answer is:

going downhill

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'getting' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.

'worse at skiing?' is the wordplay.
'worse' becomes 'downhill' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'at' is a charade indicator (letters next to each other) (I've seen this in other clues).
'skiing?' becomes 'going' (skiing is a kind of going).
'downhill' put after 'going' is 'GOING DOWNHILL'.

Can you help me to learn more?

I've seen this clue in The Times and the Sydney Morning Herald.

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