Risk backing old police force and its area of activity (5)

I believe the answer is:

incur

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

I can't explain the rest of the clue.

(Other definitions for incur that I've seen before include "Become subject to (something unpleasant)" , "Fall into - invite" , "Bring on oneself, probably unpleasant" , "contract" , "Become responsible for" .)

I've seen this clue in The Times.

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