Unity C# script to find a reference to player.

FindPlayer.cs

void Awake ()
	{
		// Setting up the reference.
		FindPlayer();

	}

	// Update is called once per frame
void Update () {

		if(player){
			// Do game logic with player 
		}else{
			FindPlayer();
		}

}

void FindPlayer(){
		playerGO = GameObject.FindGameObjectWithTag("Player");
		if(playerGO){
			player = playerGO.transform;
			Debug.Log (player);
			setupLineRenderer();
		}
}