Show-off sacrifices knight, gets into mess (7)

I believe the answer is:

egotist

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'show-off' is the definition.
(I've seen this before)

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

(Other definitions for egotist that I've seen before include "One absorbed in self" , "Boaster" , "Self-conceited person" , "One excessively conceited" , "Excessively conceited person" .)

I've seen this clue in The Hindu.

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