Would you give me a leg up?

There is no problem with the interpretation of the expression in bold in the following sentence:

She later uses this to punch her way out of a casket after being buried alive.

This in not how matters stand by the following sentence.

For decades, US administrations - both Democratic or Republican - have been complaining that the economic giant that is Europe punches way below its weight in world politics.

It is beyond me. I couldn’t define the precise interpretation in plain English. Would you give me a leg up?

Thank you for your efforts.

It’s a boxing idiom, Ivo.

If a boxer ‘punches below his weight’ he performs at a lower level than one would expect of him based on his preparation, rank, or past accomplishments.

In your sentence, the US feels that Europe has the necessary expertise and experience to take a lead in world politics, but the US complains because it doesn’t feel that European leaders do so.