"Well, basically, it's just inertia. The ball doesn't have much inertia, so a small kick (or small force) can get it moving. The harder you kick, the more speed you give it. So something moving will never stop moving (or rolling) until an object or friction,"
"In this case, the net, stops it. And what is at rest stays at rest. But if nothing stops it, it will stay at the same velocity.