Sidewalk pedestrian (4)

I believe the answer is:

crab

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'sidewalk pedestrian' is the definition.
The answer and definition can be both people as well as being singular nouns.
Maybe there's a link between them I don't understand?

This is the entire clue.

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(Other definitions for crab that I've seen before include "Sour character" , "Edible crustacean" , "terrible row" , "A crustacean; type of apple" , "A sea creature; an apple" .)

I've seen this clue in The Globe and Mail.

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