• From an Update() function use Physics.RayCast to see if the touch position intersects with the ball. Use Camera.main.ScreenPointToRay() passing the touch positions (if you are using more than one).
• Decide on whether to do the ray case when the touch begins, or all the time and only do the ray cast if the touch phase fits your expected phase(s).

• When you detect a hit you need to AddForce to the rigidbody attached to the ball. You can create a Vector3 of the lowest possible angle and the multiple a Quaternion that you make from a random rotate around whichever axis you need (maybe Z).

   var q = Quaternion.Euler(0,0,Random.Range(0,30));
   var forceDirection = q * startingVector;
  

Okay, I have almost got this working. Raycast now works and it successfully recognizes when I touch the ball. Now all I need to know is how to input the addforce.

Here is the code I'm using for the ray cast.

var particle : GameObject;
function Update () {
    for (var i = 0; i < Input.touchCount; ++i) {
        if (Input.GetTouch(i).phase == TouchPhase.Began) {
            // Construct a ray from the current touch coordinates
            var ray = Camera.main.ScreenPointToRay (Input.GetTouch(i).position);
            if (Physics.Raycast (ray)) {
                // Create a particle if hit
                Instantiate (particle, transform.position, transform.rotation);
            }
        }
    }
}

How would I add the addforce to that code? Here is the code I have for the addforce.

function FixedUpdate () {
    rigidbody.AddForce (Vector3.up * 10);
}

How would I input that code into the previous one?