BallHandler.cs

using UnityEngine;
using System.Collections;

public class BallHandler : MonoBehaviour {

    // Use this for initialization
    void Start () {
        //this gives the ball a kick when it's spawned
        rigidbody.AddForce(Vector3.right * 200 + Vector3.forward * 100);
    }
    // Update is called once per frame
    void Update () {
        //this if statement accelerates the ball until it hits a set speed
        //the acceleration rate was determined experimentally to provide a challenging speedup
        if (Mathf.Abs (rigidbody.velocity.x) < 40){
            Vector3 shrt = rigidbody.velocity;
            rigidbody.velocity = new Vector3(shrt.x + 0.001f/Time.deltaTime * Mathf.Sign(shrt.x), shrt.y, shrt.z);
        }
        //this locks the ball's y-axis and prevents it from rising or falling
        //this line is provided for instructional purposes: a better way of doing this is to place
        //a restriction on the object's rigidbody
        transform.position = new Vector3(transform.position.x, 0, transform.position.z);

    }
    //this is called when the object collides with something
    void OnCollisionEnter(Collision other){
        //this if statement gives the ball a kick in the z direction when it hits something
        //this avoids the ball getting stuck in repetitive back-and-forth patterns
        //the precise values used here were, again, determined exerimentally
        if (Mathf.Abs (rigidbody.velocity.z) < 15){
            Vector3 shrt = rigidbody.velocity;
            rigidbody.AddForce(Vector3.forward * 250 * Mathf.Sign(shrt.z));
        }
    }
}