C# Unity3D Ball Physics

using UnityEngine;
public class Player : MonoBehaviour { }
void Update () {
        Vector2 playerControls;
        playerInput.x = 0f;
        playerInput.y = 0f;
        transform.localPosition = new Vector3(playerInput.x, 1f, playerInput.y);
    playerInput.x = Input.GetAxis("Horizontal");
    playerInput.y = Input.GetAxis("Vertical");
    playerInput = Vector2.ClampMagnitude(playerInput, 2f);
    Vector3 velocity = new Vector3(playerInput.x, 0f, playerInput.y);
        Vector3 displacement = velocity * Time.deltaTime;
        transform.localPosition += displacement;
    [SerializeField, Range(1f, 1000f)]
    float maxSpeed = 20f;
    Vector3 velocity =
            new Vector3(playerInput.x, 1f, playerInput.y) * maxSpeed;
    Vector3 acceleration =
            new Vector3(playerInput.x, 0f, playerInput.y) * maxSpeed;
        velocity += acceleration * Time.deltaTime;
        Vector3 displacement = velocity * Time.deltaTime;
        [SerializeField, Range(1f, 1000f)]
    float maxAcceleration = 20f;
    Vector3 desiredVelocity =
            new Vector3(playerInput.x, 0f, playerInput.y) * maxSpeed;
        float maxSpeedChange = maxAcceleration * Time.deltaTime;
    float maxSpeedChange = maxAcceleration * Time.deltaTime;
    velocity.x =
            Mathf.MoveTowards(velocity.x, desiredVelocity.x, maxSpeedChange);
        velocity.z =
            Mathf.MoveTowards(velocity.z, desiredVelocity.z, maxSpeedChange);
    [SerializeField]
    Rect allowedArea = new Rect(-5f, -5f, 10f, 10f);
    Vector3 newPosition = transform.localPosition + displacement;
        transform.localPosition = newPosition;
    Vector3 newPosition = transform.localPosition + displacement;
        if (newPosition.x < allowedArea.xMin) {
            newPosition.x = allowedArea.xMin;
            velocity.x = -velocity.x;
        }
        else if (newPosition.x > allowedArea.xMax) {
            newPosition.x = allowedArea.xMax;
            velocity.x = -velocity.x;
        }
        if (newPosition.z < allowedArea.yMin) {
            newPosition.z = allowedArea.yMin;
            velocity.z = -velocity.z;
        }
        else if (newPosition.z > allowedArea.yMax) {
            newPosition.z = allowedArea.yMax;
            velocity.z = -velocity.z;
        }
    if (newPosition.x < allowedArea.xMin) {
            newPosition.x = allowedArea.xMin;
            velocity.x = -velocity.x * bounciness;
        }
        else if (newPosition.x > allowedArea.xMax) {
            newPosition.x = allowedArea.xMax;
            velocity.x = -velocity.x * bounciness;
        }
        if (newPosition.z < allowedArea.yMin) {
            newPosition.z = allowedArea.yMin;
            velocity.z = -velocity.z * bounciness;
        }
        else if (newPosition.z > allowedArea.yMax) {
            newPosition.z = allowedArea.yMax;
            velocity.z = -velocity.z * bounciness;
        }
    //This is a very old script I made a year ago in Unity3D and never used so apologies if it doesn't work, I just learnt it from an old YouTube tutorial so it may be broken!