There are several ways this could be accomplished, depending on the rest of your game. Here's one simple way....

Here's a script to attach to your player GameObject:

public static var instance:Player = null;

public var startingPlace:Transform; // Drag the spawn point GameObject here in the editor
public var respawnLimit:int = 3; // How many times the player can hit a sphere (this allows you to configure it in the editor)

private var respawnCount:int; // Used for counting how many times the player hits a sphere and respawns

function Awake():void {
    instance = this;
    respawnCount = 0;
}

function Respawn():void {
    if(++respawnCount > respawnLimit) {
        // Game over!
    }
    else {
        transform.position = startingPlace.position;
        transform.rotation = startingPlace.rotation;
    }
}

Here's a script to attach to your sphere GameObjects:

function OnTriggerEnter(other:Collider):void {
    Player.instance.Respawn(); // NOTE: This assumes you named the above script Player.js.  If you name it something else, replace "Player" on this line with the name of the script.
}