Those who lose control in rows may catch it (4)

I believe the answer is:

crab

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'it' is the definition.
The definition suggests a singular noun which matches the answer.

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(Other definitions for crab that I've seen before include "Pincered crustacean" , "Edible crustacean" , "Seashore crustacean" , "accidentally caught in a row?" , "Sour character" .)

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

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