Crossword Genius

Where boater may go down instantly? (2,3,4,2,1,3)

Ross

I believe the answer is:

at the drop of a hat

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

I don't understand the rest of the clue.

(Other definitions for at the drop of a hat that I've seen before include "Immediately" , "When pork pie downed" , "When a tile falls to the ground" , "instantly" , "in no time at all" .)

I've seen this clue in The Times.
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