Put an instance of "ball MC" it on stage and name it.
(in this example the instance name is "myMovie")
Create a new button (in this example it is the "arrow") and place two instances of it on stage
(in this example the right arrow is rotated by 180 degrees)
On the left button enter the following action:
on (release) {
_root.myMovie.back.gotoAndPlay("loop");
}
Since the "back MC"'s first frame stops the movie this button tells it to go to the second frame and enter the loop between the second and the third frame.
On the right button enter the following actions:
on (release) {
_root.myMovie.back.gotoAndStop(1);
_root.myMovie.play();
}
The first line stops the "back MC" and the second tells the "ball MC" to continue playing from whatever frame the ball is at.
Well that's it.
You can use this kind of stuff in a flash game or on a pictures' gallery.
I hope you'll find it useful.