Maybe Sally holds Meg back to start to boost (7)

I believe the answer is:

augment

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'to boost' is the definition.
(to augment is to boost or increase)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for augment that I've seen before include "Make greater in size, number, etc." , "Expand" , "Increase number of" , "Add to, increase" , "Enlarge or increase" .)

I've seen this clue in The Daily Express.

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