That is because of Uranus' tilt. Earth's tilt is a bit slanting while Uranus' tilt is completely horizontal, which makes it rotate on its sides.

Earth's Rotation:

The Earth spins like a top due to its initial angular momentum that was imparted during its formation. As the Earth formed from the solar nebula, the gravitational forces caused the material to collapse and start rotating. This rotation has been maintained over billions of years due to the conservation of angular momentum.

Uranus's Rotation:

Uranus spins like a ball due to a unique set of circumstances in its formation and history. Unlike Earth, Uranus is tilted on its side, with its axis of rotation almost parallel to its orbital plane. This extreme tilt is thought to be a result of a giant impact early in Uranus's history, causing it to rotate differently than the other planets.

Key Differences:
- Earth's rotation is relatively stable and aligned with its orbital plane, giving it a top-like spinning motion.
- Uranus's rotation is tilted and erratic, giving it a ball-like spinning motion.

In conclusion, the different spinning motions of Earth and Uranus can be attributed to their respective formation histories and unique characteristics. While Earth's rotation is relatively stable and predictable, Uranus's rotation is tilted and erratic, making it spin like a ball.