DragLaunch.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

[RequireComponent (typeof(Ball))]
public class DragLaunch : MonoBehaviour {

	private Ball ball;
	private Vector3 dragStart, dragEnd;
	private float startTime, endTime;

	// Use this for initialization
	void Start () {
		ball = GetComponent<Ball>();
	}

	public void DragStart(){
		// Capture time and position of mouse click
		dragStart = Input.mousePosition;
		startTime = Time.time;
	}

	public void DragEnd(){
		// Launch the ball
		dragEnd = Input.mousePosition;
		endTime = Time.time;

		float dragDuration = endTime - startTime;
		float launchSpeedX = (dragEnd.x - dragStart.x) / dragDuration; 
		float launchSpeedZ = (dragEnd.y - dragStart.y) / dragDuration;

		Vector3 launchVelocity = new Vector3(launchSpeedX, 0, launchSpeedZ);

		if(!ball.ballLaunched){
			ball.Launch(launchVelocity);
		}
	}

	public void MoveStart(float xNudge){
		if(!ball.ballLaunched){
			float xPos = Mathf.Clamp(ball.transform.position.x + xNudge, -51, 51);
			float yPos = ball.transform.position.y;
			float zPos = ball.transform.position.z;
			ball.transform.position = new Vector3(xPos, yPos, zPos);
		}
	}
}