Also jumpshot. Any shot where the cue ball is intentionally jumped into the air to clear an obstacle (usually an object ball, even in games with non-ball objects, e.g. bottle pool). Jump shots must be performed by hitting the cue ball into the table's surface so that it rebounds from the cloth. Scooping under the cue ball to fling it into the air is deemed a foul by all authoritative rules sources, as the cue ball is technically struck twice, once by the tip, once by the ferrule. A legaljumpshot works by compressing the cue ball slightly against the slate under the cloth, causing it to spring upward when the downward pressure of the cue is released. Naturally, non-standard "rock" cue balls (made of ceramic, much denser than the more typical phenolic resin and other plastics used for billiard balls) are not well-suited to jump shots. Some billiard halls and even entire leagues prohibit all jump (and usually also massé) shots, out of fears of damage to the equipment, especially the cloth. Specialized jump cues exist to better facilitate jump shots; they are usually shorter and lighter, and with harder tips, than normal cues. Jump shots that go through or into objects rather than over them are common in trick shot (artistic pool and artistic billiards) competition.