Why the ball rolls by itself

I am trying to hit a ball with a golf club.
Ball's inspector and club head inspector can be seen in the attached images.

Then ball and club head have sphere colliders and I am expecting they collide each other.
I properly position the ball just in front of the head in the program

Vector3 loc = head.GetComponent<Collider>().bounds.center;
loc.x = loc.x - 0.15f;
head.transform.position = loc;
Instantiate(Ball, head.position, head.rotation);

So at the start of the application in running, the ball is located at in front of the head (please see in the attached image). But after a while, the ball rolls to that direction by itself as in another image.

I am expecting the two object collide and see in Debug.Log as

public class PassHeadScript : MonoBehaviour
{

void OnCollisionEnter(Collision collision)
{

if (collision.gameObject.name == "Ball(Clone)")
{

Debug.Log("Collided with ball");​

}​

}​

}

public class BallScript : MonoBehaviour {

void OnCollisionEnter(Collision collision){

if (collision.gameObject.name == "AW52_Head")
{

Debug.Log("Collided with club head");​

}​

}​

}
My queries are
Why the ball rolls by itself when the application runs?
Is that the right way to debug as the two objects collide?

Thanks

EDIT:

Now I found out that when I set ball rigidbody's drag and angular drag to 2. It doesn't roll. But it doesn't print Debug Log from both ball and club head during animation of club swing.