Upset? Depends how big-headed one is (7)

I believe the answer is:

capsize

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'upset?' is the definition.
(I've seen this before)

I can't explain the rest of the clue.

(Other definitions for capsize that I've seen before include "Upset" , "Turn so that keel faces upwards" , "Of boat, turn turtle" , "Overturn (a boat)" .)

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

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