As a sport

At least the games with regulated international professional competition have been referred to as "sports" or "sporting" events, not simply "games", since 1893 at the latest. Quite a variety of particular games (i.e. sets of rules and equipment) are the subject of present-day competition, including many of those already mentioned, with competition being especially broad in nine-ball, snooker, three-cushion and eight-ball.

Snooker, though technically a pocket billiards variant and closely related in its equipment and origin to the game of English billiards, is a professional sport organized at the international level, and its rules bear little resemblance to those of pool games.

A "Billiards" category encompassing pool, snooker and carom was featured in the 2005 World Games, held in Duisburg, Germany, and the 2006 Asian Games also saw the introduction of a "Cue sports" category. (wikipedia)

Major Games

There are two main varieties of billiard games: carom and pocket. The main carom billiards games are straight billiards, balkline and three cushion billiards. All are played on a pocketless table with three balls; two cue balls and one object ball. In all, players shoot a cue ball so that it makes contact with the opponent's cue ball as well as the object ball.

The most popular of the large variety of pocket games are eight-ball, nine-ball, one-pocket, bank pool, snooker and, among the old guard, straight pool. In eight-ball and nine-ball the object is to sink object balls until one can legally pocket the winning eponymous "money ball". Well-known but waning in popularity is straight pool, in which players seek to continue sinking balls, rack after rack if they can, to reach a pre-determined winning score (typically 150). Related to nine-ball, another well-known game is rotation, where the lowest-numbered object ball on the table must be struck first, although any object ball may be pocketed (i.e., combination shot). Each pocketed ball is worth its number, and the player with the highest score at the end of the rack is the winner. Since there are only 120 points available (1 + 2 + 3 ? + 15 = 120), scoring 61 points leaves no opportunity for the opponent to catch up. In both one-pocket and bank pool, the players must sink a set number of balls; respectively, all in a particular pocket, or all by bank shots. In snooker, players score points by alternately potting red balls and various special "colour balls".

Straight rail or straight billiards

In straight rail, a player scores a point and may continue shooting each time his cue ball makes contact with both other balls.

Although a difficult and subtle game, some of the best players of straight billiards developed the skill to gather the balls in a corner or along the same rail for the purpose of playing a series of nurse shots to score a seemingly limitless number of points.

The first straight rail professional tournament was held in 1879 where Jacob Schaefer, Sr. scored 690 points in a single turn (that is, 690 separate strokes without a miss). With the balls repetitively hit and barely moving in endless "nursing", there was little for the fans to watch.

Balkline

In light of these phenomenal skill developments in straight rail, the game of balkline soon developed to make it impossible for a player to keep the balls gathered in one part of the table for long, greatly limiting the effectiveness of nurse shots. A balkline (not to be confused with baulk line, which pertains to the game of English billiards) is a line parallel to one end of a billiards table. In the games of balkline – 18.1 and 18.2 (pronounced "eighteen-point-two") balkline, among other more obscure variations – the players have to drive at least one object ball past a balkline set at 18 inches (460 mm) from each rail, after one or two points have been scored, respectively.

Three cushion Billiards

A more elegant solution was three-cushion billiards, which requires a player to make contact with the other two balls on the table and contact three rail cushions in the process. This is difficult enough that even the best players can only manage to average one to two points per turn.

English Billiards

Dating to approximately 1800, English billiards is a hybrid of carom and pocket billiards played on a 6-foot (1.8 m) by 12-foot (3.7 m) table. Like most carom games, it requires two cue balls and a red object ball. The object of the game is to score either a fixed number of points, or score the most points within a set time frame, determined at the start of the game.

Points are awarded for:

* Two-ball cannons: striking both the object ball and the other (opponent's) cue ball on the same shot (2 points)
* Winning hazards: potting the red ball (3 points); potting the other cue ball (2 points)
* Losing hazards (or "in-offs"): potting one's cue ball by cannoning off another ball (3 points if the red ball was hit first; 2 points if the other cue ball was hit first, or if the red and other cue ball were "split", i.e. hit simultaneously).

Snooker

Snooker is a pocket billiards game originated by British officers stationed in India during the 19th century. The name of the game became generalized to also describe one of its prime strategies: to "snooker" the opposing player by causing that player to foul or leave an opening to be exploited.

In the United Kingdom, snooker is by far the most popular cue sport at the competitive level. It is played in many other countries as well. Snooker is far rarer in the U.S., where pool games such as eight-ball and nine-ball dominate. The first International Snooker Championship was held in 1927, and it has been held annually since then with few exceptions. The World Professional Billiards and Snooker Association (WPBSA) was established in 1968 to regulate the professional game, while the International Billiards and Snooker Federation (IBSF) regulates the amateur games.

Eight Ball

In the United States, the most commonly-played game is eight-ball. The goal of eight-ball, which is played with a full rack of fifteen balls and the cue ball, is to claim a suit (commonly stripes or solids in the US, and reds or yellows in the UK), pocket all of them, then legally pocket the 8 ball, while denying one's opponent opportunities to do the same with their suit, and without sinking the 8 ball early by accident. On the professional scene, eight-ball players on the International Pool Tour (IPT) were the highest paid players in the world as of 2006 (the IPT nearly folded in 2007, and as of 2008 is attempting a comeback). In the United Kingdom the game is commonly played in pubs, and it is competitively played in leagues on both sides of the Atlantic. The most prestigious tournaments including the World Open are sponsored and sanctioned by the International Pool Tour. Rules vary widely from place to place (and between continents to such an extent that British-style eight-ball pool/blackball is properly regarded as a separate game in its own right). Pool halls in North America are increasingly settling upon the World Pool-Billiard Association International Standardised Rules. But tavern eight-ball (also known as "bar pool"), typically played on smaller, coin-operated tables and in a "winner keeps the table" manner, can differ significantly even between two venues in the same city. The growth of local, regional and national amateur leagues may alleviate this confusion eventually.

Nine Ball

Nine-ball uses only the 1 through 9 balls and cue ball. It is a rotation game: The player at the table must make legal contact with the lowest numbered ball on the table or a foul is called. The game is won by legally pocketing the nine ball. Nine-ball is the predominant professional game, though as of 2006–2008 there have been some suggestions that this may change, in favor of ten-ball.[clarification needed] There are many local and regional tours and tournaments that are contested with nine-ball. The World Pool-Billiard Association (WPA), and it American affiliate the Billiard Congress of America (BCA), publish the World Standardized Rules. The European professional circuit has instituted rules changes, especially to make it more difficult to achieve a legal break shot. The largest nine-ball tournaments are the independent US Open Nine-ball Championship and the WPA World Nine-ball Championship for men and women. Male professionals have a rather fragmented schedule of professional nine-ball tournaments. The United States Professional Pool Players Association (UPA) has been the most dominant association of the 1990s and 2000s. A hotly contested event is the annual Mosconi Cup, which pits invitational European and US teams against each other in one-on-one and scotch doubles nine-ball matches over a period of several days. The Mosconi Cup games are played under the more stringent European rules, as of 2007.

Three ball

A variant using only three balls, generally played such that the player at turn continues shooting until all the balls are pocketed, and the player to do so in the fewest shots wins. The game can be played by two or more players. Dispenses with some fouls common to both nine- and eight-ball.

One-pocket

One-pocket is a strategic game for two players. Each player is assigned one of the corner pockets on the table. This is the only pocket into which he can legally pocket balls. The first player to pocket the majority of the balls (8) in his pocket wins the game. The game requires far more defensive strategy than offensive strategy, much unlike eight-ball, nine-ball, or straight pool. It has been said[weasel words] that if eight-ball is checkers, one-pocket is chess. This statement can be verified by watching a game of one pocket. Most times, accomplished players choose to position balls near their pocket instead of trying to actually pocket them. This allows them to control the game by forcing their opponent to be on defense instead of taking a low percentage shot that could result in a loss of game. These low percentage shots are known as "flyers" by one pocket aficionados.

Bank pool

Bank pool has been gaining popularity in recent years. Bank pool can be played with a full rack (can be a long game), but is more typically played with nine balls (frequently called "nine-ball bank"). The balls are racked in nine-ball formation, but in no particular order. The object of the game is simple: to be the first player to bank five balls in any order (eight balls when played with a full rack). Penalties and fouls are similar to one pocket in that the player committing the foul must spot a ball for each foul. This must be done before the incoming player shoots.

Speed pool

Speed pool is a standard billiards game where the balls must be pocket in as little time as possible. Rules vary greatly from tournament to tournament. The International Speed Pool Challenge has been held annually since 2006. (wikipedia)