Large frame on boxer boosted advantage (3-2)

I believe the answer is:

leg-up

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

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

I don't understand how the remainder of the clue works.

(Another definition for leg-up that I've seen is " A boost to improve one's position".)

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

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