Coordinate confusion

I attached the following script to a ball. When I run the script, it always launches towards the camera. Why is that?

and how often does function update() cycle? Once a second?

var time = 0;
var x =0;
var y =0;
var velx = 4;
var vely = 300;

function Update ()
    x = velx * time;
    y = vely * time - 0.5*9.8*time*time;
    transform.position = Vector3(0,y,x);

Update runs every frame. This makes your code framerate-dependent; use Time.deltaTime to fix that. The ball is only doing what you to told it to do...I'm not sure what your intentions were.