A nut case it's said involved in a row (5)

I believe the answer is:

scull

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'a row' is the definition.
(I've seen this before)

I don't understand how the remainder of the clue works.

(Other definitions for scull that I've seen before include "Small oar" , "A single oar" , "Blade" , "Row with two oars" , "Light rowing boat" .)

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

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