A spear-thrower or atlatl ( or ; Nahuatl languages: ahtlatl; Nahuatl pronunciation: ['a?tat]) is a tool that uses leverage to achieve greater velocity in dart-throwing, and includes a bearing surface which allows the user to store energy during the throw.
It may consist of a shaft with a cup or a spur at the end that supports and propels the butt of the dart. The spear-thrower is held in one hand, gripped near the end farthest from the cup. The dart is thrown by the action of the upper arm and wrist. The throwing arm together with the atlatl acts as a lever. The spear-thrower is a low-mass, fast-moving extension of the throwing arm, increasing the length of the lever. This extra length allows the thrower to impart force to the dart over a longer distance, thus imparting more energy and ultimately higher speeds.
Common modern ball throwers (molded plastic shafts used for throwing tennis balls for dogs to fetch) use the same principle.
A spear-thrower is a long-range weapon and can readily impart to a projectile speeds of over 150 km/h (93 mph).
Spear-throwers appear very early in human history in several parts of the world, and have survived in use in traditional societies until the present day, as well as being revived in recent years for sporting purposes. In the United States the Nahuatl word atlatl is often used for revived uses of spear-throwers, and in Australia the Aboriginal word woomera.
Spear-thrower designs may include improvements such as thong loops to fit the fingers, the use of flexible shafts, stone balance weights, and thinner, highly flexible darts for added power and range. Darts resemble large arrows or thin spears and are typically from 1.2 to 2.7 m (4 to 9 ft) in length and 9 to 16 mm (3/8" to 5/8") in diameter.
Another important improvement to the spear-thrower's design was the introduction of a small weight (between 60 and 80 grams) strapped to its midsection. Some atlatlists maintain that stone weights add mass to the shaft of the device, causing resistance to acceleration when swung and resulting in a more forceful and accurate launch of the dart. Others claim that spear-thrower weights add only stability to a cast, resulting in greater accuracy.
Based on previous work done by William S. Webb, William R. Perkins claims that spear-thrower weights, commonly called "bannerstones", and characterized by a centered hole in a symmetrically shaped carved or ground stone, shaped wide and flat with a drilled hole and thus a little like a large wingnut, are a rather ingenious improvement to the design that created a silencing effect when swung. The use of the device would reduce the telltale "zip" of a swung atlatl to a more subtle "woof" sound that did not travel as far and was less likely to alert prey. Robert Berg's theory is that the bannerstone was carried by hunters as a spindle weight to produce string from natural fibers gathered while hunting, for the purpose of tying on fletching and hafting stone or bone points.
The woomera design is distinctly different from most other spear-throwers, in that it has a curved, hollow shape, which allows for it to be used for other purposes.
Several Stone Age spear-throwers (usually now incomplete) are decorated with carvings of animals: the British Museum has a mammoth, and there is a hyena in France. Many pieces of decorated bone may have belonged to Bâtons de commandement.
Wooden darts were known at least since the Middle Paleolithic (Schöningen, Torralba, Clacton-on-Sea and Kalambo Falls). While the spear-thrower is capable of casting a dart well over one hundred meters, it is most accurately used at distances of twenty meters or less. The spearthrower is believed to have been in use by Homo sapiens since the Upper Paleolithic (around 30,000 years ago). Most stratified European finds come from the Magdalenian (late upper Palaeolithic). In this period, elaborate pieces, often in the form of animals, are common. The earliest secure data concerning atlatls have come from several caves in France dating to the Upper Paleolithic, about 21,000 to 17,000 years ago. The earliest known example is a 17,500-year-old Solutrean atlatl made of reindeer antler, found at Combe Saunière (Dordogne), France. It is possible that the atlatl was invented earlier than this, as Mungo Man from 42 000 BP displays arthritis in his right elbow, a pathology referred today as the "Atlatl elbow," resulting from many years of forceful torsion from using an atlatl.  At present there is no evidence for the use of atlatls in Africa. Peoples such as the Maasai and Khoi San throw spears without any aids, but its use in hunting is limited in comparison to the spear thrower since the animal must be very close and already immobile.
In Europe, the spear-thrower was supplemented by the bow and arrow in the Epi-Paleolithic. Along with improved ease of use, the bow offered the advantage that the bulk of elastic energy is stored in the throwing device, rather than the projectile; arrow shafts can therefore be much smaller, and have looser tolerances for spring constant and weight distribution than atlatl darts. This allowed for more forgiving flint knapping: dart heads designed for a particular spear thrower tend to differ in mass by only a few percent. By the Iron Age, the amentum, a strap attached to the shaft, was the standard European mechanism for throwing lighter javelins. The amentum gives not only range, but also spin to the projectile.
The spear-thrower was used by early Americans as well. It seems to have been introduced to America during the immigration across the Bering Land Bridge, and despite the later introduction of the bow and arrow, atlatl use was widespread at the time of first European contact. Complete wooden spear-throwers have been found on dry sites in the western United States and in waterlogged environments in Florida and Washington. Several Amazonian tribes also used the atlatl for fishing and hunting. Some even preferred this weapon over the bow and arrow, and used it not only in combat but also in sports competitions. Such was the case with the Tarairiu, a Tapuya tribe of migratory foragers and raiders inhabiting the forested mountains and highland savannahs of Rio Grande do Norte in mid-17th-century Brazil. Anthropologist Harald Prins offers the following description:
The atlatl, as used by these Tarairiu warriors, was unique in shape. About 88 cm (35 in) long and 3 to 4.5 cm ( to in) wide, this spear thrower was a tapering piece of wood carved of brown hard-wood. Well-polished, it was shaped with a semi-circular outer half and had a deep groove hollowed out to receive the end of the javelin, which could be engaged by a horizontal wooden peg or spur lashed with a cotton thread to the proximal and narrower end of the throwing board, where a few scarlet parrot feathers were tied for decoration. [Their] darts or javelins ... were probably made of a two-meter long wooden cane with a stone or long and serrated hard-wood point, sometimes tipped with poison. Equipped with their uniquely grooved atlatl, they could hurl their long darts from a great distance with accuracy, speed, and such deadly force that these easily pierced through the protective armor of the Portuguese or any other enemy.
Among the Tlingit of Southeast Alaska, approximately one dozen very old elaborately carved specimens they call "shee áan" (sitting on a branch) remain in museum collections  and private collections, one having sold at auction for more than $100,000.
In September 1997, a atlatl dart fragment, carbon dated to 4360 ± 50 14C yr BP (TO 6870), was found in an ice patch on mountain Thandlät, the first of the southern Yukon Ice Patches to be studied.:363:2
As well as its practical use as a hunting weapon, it may also have had social effects. John Whittaker, an anthropologist at Grinnell College, Iowa, suggests the device was a social equalizer in that it requires skill rather than muscle power alone. Thus women and children would have been able to participate in hunting, although in recent Australian societies, spear-throwers are restricted by custom to male use.
Whittaker said the stone-tipped projectiles from the Aztec atlatl were not powerful enough to penetrate Spanish steel plate armor, but they were strong enough to penetrate the mail, leather and cotton armor that most Spanish soldiers wore. Whittaker said the Aztecs started their battles with atlatl darts followed with melee combat using the macuahuitl.
Another type of Stone Age artefact that is sometimes excavated is the bâton de commandement. These are shorter, normally less than one foot long, and made of antler, with a hole drilled through them. When first found in the nineteenth century, they were interpreted by French archaeologists to be symbols of authority, like a modern Field Marshal's baton, and so named bâtons de commandement ("batons of command"). Though debate over their function continues, tests with replicas have found them, when used with a cord, very effective aids to spear or dart throwing. Another theory is that they were "arrow-straighteners".
In modern times, some people have resurrected the dart thrower for sports, often using the term atlatl, throwing either for distance and/or for accuracy. The World Atlatl Association was formed in 1987 to promote the atlatl. Throws of almost 260 m (850 ft) have been recorded. Colleges reported to field teams in this event include Grinnell College in Iowa, Franklin Pierce University in New Hampshire, Alfred University in New York, and the University of Vermont.
Atlatls are sometimes used in modern times for hunting. In the U.S., the Pennsylvania Game Commission has given preliminary approval for legalization of the atlatl for hunting certain animals. The animals that would be allowed to atlatl hunters have yet to be determined, but particular consideration has been given to deer. Currently, Alabama allows the atlatl for deer hunting, while a handful of other states list the device as legal for rough fish (those not sought for sport or food), some game birds and non-game mammals. Starting in 2007, Missouri allowed use of the atlatl for hunting wildlife (excluding deer and turkey), and starting in 2010, also allowed deer hunting during the firearms portion of the deer season (except the muzzleloader portion). Starting in 2012, Missouri allowed the use of atlatls during the fall archery deer and turkey hunting seasons and, starting in 2014, allowed the use of atlatls during the spring turkey hunting season as well. Missouri also allows use of the atlatl for fishing, with some restrictions (similar to the restrictions for spearfishing and bowfishing). The Nebraska Game and Parks Commission allows the use of atlatls for the taking of deer as of 2013 .
The woomera is still used today by some Australian Aborigines for hunting in remote parts of Australia. Yup'ik Eskimo hunters still use the atlatl, known locally as "nuqaq" (nook-ak), in villages near the mouth of the Yukon River for seal hunting.
There are numerous atlatl competitions held every year, with spears and spear-throwers built using both ancient and modern materials. Events are often held at parks, such as Letchworth State Park in New York, Cahokia Mounds State Historic Site in Illinois, or Valley of Fire State Park in Nevada. Atlatl associations around the world host a number of local atlatl competitions. Chimney Point State Historic Site in Addison, Vermont hosts the annual Northeast Open Atlatl Championship. In 2009, the Fourteenth Annual Open Atlatl Championship was held on Saturday and Sunday, September 19 and 20. On the Friday before the Championship, a workshop was held to teach modern and traditional techniques of atlatl and dart construction, flint knapping, hafting stone points, and cordage making. Competitions may be held in conjunction with other events, such as the Ohio Pawpaw Festival, or at the Bois D'Arc Primitive Skills Gathering and Knap-in, held every September in southern Missouri.
Atlatl events commonly include the International Standard Accuracy Competition (ISAC), in which contestants throw ten times at a bull's-eye target. Other contests involving different distances or terrain may also be included, usually testing the atlatlist's accuracy rather than distance throwing.
In the sixth episode of the fourth season of the television competition Top Shot, the elimination round consisted of two contestants using the atlatl at ranges of 30, 45 and 60 feet.