Leaving rest unprepared (3,7)

I believe the answer is:

off balance

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

'leaving rest' is the wordplay.
'leaving' becomes 'off' (I've seen this in other clues).
'rest' becomes 'balance' (I've seen this before).
'off'+'balance'='OFF BALANCE'

(Other definitions for off balance that I've seen before include "Not prepared" , "unprepared" .)

I've seen this clue in The Telegraph.

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