Swell to head off violent larcenies (8)

I believe the answer is:

increase

I'm a little stuck... Click here to teach me more about this clue!

'swell' is the definition.
(I've seen this in another clue)

I don't understand the rest of the clue.

(Other definitions for increase that I've seen before include "Grow in size" , "Grow greater" , "Become greater in number" , "Add, make bigger" , "Make larger in a sincere way" .)

I've seen this clue in the Sydney Morning Herald.

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