Crossword Genius

Move over, easily demolishing lead of marathon runner (3)

Ross

I believe the answer is:

ski

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'runner' is the definition.
(ski is a kind of runner)

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for ski that I've seen before include "Piece of sports equipment" , "Winter sport item" , "Pole? How one often ends" , "Engage in a winter sport" , "Go downhill rapidly" .)

I've seen this clue in The Telegraph.
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