Cheat cornered on the board (4)

I believe the answer is:

rook

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'cheat' is the definition.
(I know that rook is a type of cheat)

I can't explain the rest of the clue.

(Other definitions for rook that I've seen before include "flier" , "man in marginalised position, initially" , "Man in game" , "Another name for castle in chess" , "embattled man" .)

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

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