I would like to destroy a Dyson Sphere so it leaves big chunks of scrap metal with no habitable zones left, but still with enough structure to hold building-sized blocks.

The destruction shouldn't be man made.

Sphere Description (ordered from the sun to the outer layers):

1. Habitable Zone: cities, agricultural farms, places
2. Support Zone: electricity and water supply, first structure level
3. Main structure: the other structure levels where everything is built on.
4. Spaceports and Cargo System: an infrastructure on the outside where spaceships can dock and a network of "Trains" transport cargo
5. Shield Pylons: for shielding the whole Thing against little meteoroids and ships.

I've described the hull of the sphere about 200 - 500 meters thick.

What could make such an impact on the Sphere? How would the destruction progress after the initial "blow" hit the Sphere?

ETA: This question has been refocused slightly, as such some of the answers below are a little out of date.