NullReference Error for Fall Damage

Hey there Unity! So when I run the game i get spammed with the following error:
"NullReferenceException: Object reference not set to an instance of an object
FallDamage.Update () (at Assets/The Scripts/FallDamage.cs:20)"

from this script in C#, I made a comment where the error should be:

public class FallDamage : MonoBehaviour {

public GameObject player;
private ThePlayer playerScript;

public float minFall = 2.0f;
public float airTime = 0.0f;

private CharacterController _controller;

private void start(){
_controller = GetComponent<CharacterController>();
playerScript = player.GetComponent<ThePlayer>();
}

void Update(){
if(!_controller .isGrounded){ // This is line 20 which is the cause of the error.
airTime += Time.deltaTime;
}
if(_controller .isGrounded){
if(airTime > minFall)
{
playerScript.currentHealth -= 2 * airTime;
}
airTime = 0;
}
}
}

 

The proper method is "Start()", not "start()". It's case sensitive.

 

Oh... My...
Wau... How can I over see that xD