From a hitter's perspective, the curveball will start in one location (usually high or at the top of the strike zone) and then dive rapidly as it approaches the plate. The most effective curveballs will start breaking at the apex of the arc of the ball flight, and continue to break more and more rapidly as they approach and cross through the strike zone. A curveball that a pitcher fails to put enough spin on will not break much and is colloquially called a "hanging curve". Hanging curves are usually disastrous for a pitcher because the low velocity, non-breaking pitch arrives high in the zone where hitters can wait on it and drive it for power.