Crossword Genius

Is unsuited for running fast (7)

Ross

I believe the answer is:

streaks

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'is' is the definition.
Although both the answer and definition are verbs in their -s form, I don't see how they can define each other.

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for streaks that I've seen before include "Skaters (anag.)" , "Runs naughtily nude in public" , "Stripes for skaters" .)

I've seen this clue in the Evening Standard.
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