One going quietly on foot? (7)

I believe the answer is:

sneaker

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But I can't explain it at all! Could you help me understand?

(Other definitions for sneaker that I've seen before include "Soft shoe" , "American trainer" , "Casual shoe" , "one tending to go unnoticed?" , "Trainer (shoe)" .)

I've seen this clue in the Evening Standard.

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