Rigidbody/CharacterController keeps moving left

I have been following many tutorials, none have helped.
I have created a simple cube/plane, and added a ball on top of it, with a rigidbody.
Next, I have added a script, that I got from a tutorial, which rotates the ball left and right.

#pragma strict

var rotationSpeed = 100;

function Update () {
var rotation : float = Input.GetAxis ("Horizontal") * rotationSpeed;
rotation *= Time.deltaTime;
rigidbody.AddRelativeTorque(Vector3.back * rotation);

When I started the game, the ball kept moving left. The Horizontal input is at default. I also tried it with a CharacterController (different code) and it did the exact same thing.

Unplug (or calibrate) any joysticks you have attached.