Use the shortest shutter speed you can. The blur comes from very high relative motion, so this is essentially like photographing a very fast subject from a fixed position.

To make that possible, you’ll usually need:

• lots of light
• a wide aperture
• higher ISO or other high-sensitivity capture settings

For a thrown object, timing is critical, so continuous/burst shooting will improve your chances.

If the subject is moving across your frame, panning can also help: track the subject’s motion so its movement relative to the camera is reduced. This takes practice, and it’s more practical for the other train than for a small thrown object.

There’s no editing trick that can fully recover motion blur after the fact; the key is capturing enough sharpness in-camera with fast shutter speed and good timing.