Nine-ball (sometimes written 9-ball) is a contemporary form of pool (pocket billiards), with historical beginnings rooted in the United States and traceable to the 1920s. The game may be played in social and recreational settings by any number of players (generally one-on-one) and subject to whatever rules are agreed upon beforehand, or in league and tournament settings in which the number of players and the rules are set by the sponsors. During much of its history, nine-ball has been known as a "money game" in both professional and recreational settings, but has since become established as a legitimate alternative to eight ball, straight pool and other major competition games.
In recent decades, nine-ball has become the dominant tournament game in professional pool, in the World Pool-Billiard Association, Women's Professional Billiard Association and United States Professional Poolplayers Association. Matches proceed quickly, suitable for the time constraints of television coverage, and the fast-paced games tend to keep the audience engaged.
The game is played on a pocket billiards table with six pockets and with ten balls. The cue ball, which is usually a solid shade of white (but may be spotted in some tournaments), is struck to hit one or more of the other nine balls (often referred to as object balls), each of which is distinctly colored and numbered 1 through 9. The object of the game is to legally pocket the 9-ball.
In nine-ball, except when a push-out has been invoked, a legal shot consists of striking the cue ball into the lowest numbered object ball on the table and subsequently either pocketing an object ball, or driving any ball (including the cue ball) to any rail, otherwise the shot is a foul. Additional conditions apply for the break shot (see below). Object balls do not have to be pocketed in numerical order; Any ball may be pocketed at any time during the game, so long as the lowest-numbered ball is contacted first by the cue ball. Nine-ball is not a call shot game. The 9-ball itself can be legally pocketed for a win at any turn in the game, intentionally or by chance, including the break shot. Conversely, a player could potentially pocket all of the object balls numbered one through eight during the course of the game and lose after his opponent pockets only the nine-ball.
Players alternate innings at the table, meaning play continues by one player until he or she misses, commits a foul, or pockets the 9 ball for the win. The penalty for a foul is that the player's inning ends and the opponent comes to the table with ball in hand, able to place the cue ball anywhere on the table prior to shooting.
Nine-ball is a relatively fast-paced game and is rarely played by the rack. Instead, players normally play a match (or race) to a set number of games, often five, seven or nine. The first player to win that set number of games wins the match.
The rack 
The object balls are placed in a diamond-shaped configuration, with the 1 ball positioned at the front (toward the position of the breaking player) on the foot spot, and the 9 ball placed in the center. The physical rack used to position the balls is typically triangle-shaped, usually wood or plastic, and capable of holding all fifteen object balls, although diamond-shaped racks that hold only nine balls are sometimes used. The placement of the remaining balls is generally considered to be random. However, in some handicapped tournaments, the ball being spotted to the lesser player must be one of the two balls placed behind the 1 ball at the apex of the rack. An imaginary line drawn through the one-ball and back apex of the diamond should be parallel to the long rails of the table (perpendicular to the short rails). The placement of balls is expected to be precise, especially in league and tournament play; If any ball in the rack does not touch each adjacent ball, or if the rack is not "straight", or if the 1 ball is not resting precisely on the foot spot, the player assigned the break may demand a re-rack. (See also "European alterations", below, for a recently devised "template-trained" racking system.)
The break 
One person is chosen to shoot first, by breaking the rack. Usually this is determined by flipping a coin, or by lagging, especially in professional tournaments in the case of the latter, or it may be ruled by the authority in charge, the sponsor or the players themselves that the winner or loser of the previous game will always shoot first in the next rack. As with most pocket billiard games, the base of the cue ball must be behind the head string for the break shot. If the player who breaks fails to make a legal break, the opponent can either demand a re-rack and become the breaker, or continue to play as if it had been an ordinary foul, depending upon the rules of the event. If the breaker pockets a ball and commits no foul, it remains the breaker's turn. If the breaker pockets the 9 ball on the break (without fouling), this is an instant win. (See also "European alterations", below, for recent moves to change the breaking rules.)
The push-out 
After the break (regardless of its result), before the second shot of the game, the player at the table may call a "push-out." A push-out can be called by the breaking player if he legally pocketed a ball on the break, or the non-breaking player if no ball was pocketed on the break. Calling a push-out for the shot after the break allows the player taking the shot to legally hit the cue ball in almost any fashion with no foul, with the exception that the cue ball must stay on the table and illegal shots such as double-hitting the cue ball or a "scoop jump shot" should still be called a foul. The main purpose of the push-out shot is to alleviate an unlucky lie after the break, where it is difficult to make a legal shot. Unlike any other shot of the game, for a push-out shot, the cue ball is not required to contact any object ball and if an object ball is contacted, it is not required to be the lowest numbered ball. If the nine-ball is pocketed on a push-out shot it is spotted, however any other pocketed object ball stays down. A push-out should be called so that the opponent or referee hears the call, and it is customary for the opponent or referee to confirm that he heard the push-out call, so that there is no controversy surrounding the shot. After a push-out shot was called and played, the incoming player has the choice of accepting the table as it lies, or forcing the pushing-out player to take the next shot of the game (always the third shot of the game). Only one push-out is allowed per game, and it must be immediately after the break. (See also "The rise of 'Texas express' rules", below, for the historical multi-push-out rule variation.) If the pushing-out player has a particular type of shot he feels comfortable with, such as a jump shot, or two-rail bank shot, it may be strategical to leave that type of shot after the push-out. The ideal push-out shot leaves a lie that the opponent believes likely to be makeable, and will accept, but will fail to actually make, giving control of the table back to the pusher-out, and which the pusher-out is confident to make if the shot is passed back to him. Thus nine-ball players aim for a push-out that has about a 50/50 chance of being accepted or returned.
Winning a game occurs any time a player hits the lowest numbered ball first and pockets the 9-ball without committing a foul. When only the 9-ball is on the table, this is straightforward and obvious; however, when other balls remain on the table, any number of events can result in victory so long as the above requirements are met. Loss of game can occur if three successive fouls are committed and the fouling player is warned audibly or visually after the 2nd foul during the third inning.
In most rule systems, including those of the World Pool-Billiard Association and its national affiliates like the Billiard Congress of America, if a player fouls and pockets the 9 ball, or knocks the 9 ball off the table, the 9 ball is placed on the foot spot, and the incoming player receives ball-in-hand.
Rule variations and governing bodies 
The general rules the game is played under are fairly consistent and usually do not stray too far from the format set forth in the Billiard Congress of America (BCA) BCA World Standardized Rules for Nine Ball, which have merged with those of the World Pool-Billiard Association (WPA), to form the World Standardised Rules, although amateur league play may be governed by similar but slightly different rules promulgated by the American Poolplayers Association (APA) and other organizations.
The rise of "Texas express" rules 
For much of its history nine-ball rules allowed participants to "push out" multiple times during a game (see "The push-out", above, for the modern push-out rules), meaning any player could call a "push-out", and then hit the cue ball to any area on the table without being penalized by normal foul rules, such as failure to contact the lowest-numbered ball on the table. However, once a push-out was called and executed, the incoming player had the right to shoot or give the inning back to the opponent. If the player shooting the resulting shot fouled, the other player would have ball-in-hand; hence this manner of play was called the "two-foul" version. "One-foul" became popular in the 1970s, as play turned more aggressive for the early televised matches. This newer version of nine-ball awarded ball-in-hand on any cue ball foul. A now-standard rule variant, which started to sweep the sport of nine-ball in the mid-1980s, restricted the push-out option to once per game and only to the inning immediately following the break. This change profoundly affected the way the game was played. By about 1990 this new push-out rule had become ubiquitous and it and any additional rules appended to it were collectively referred to as "Texas express" rules, so called because of the supposed US state of origin and the speeding up of the game. Today, Texas express push-out rules dominate the way nine-ball is played and is the variant incorporated into the official rules maintained by the WPA and its affiliates like the BCA.
European alterations 
As of the 2000s, the rules have been somewhat in flux in certain contexts, especially in Europe. The European Pocket Billiard Federation (EPBF), BCA's WPA-affiliate counterpart in Europe, has done away with standardized racking techniques, and instead relies upon divots in the cloth to position the balls, with no physical ball rack required; these indentations are carefully created using a "training template", such that the divots are slightly closer together than they would be expected to be, thus creating ball-on-ball pressure as the balls settle partially into the divot pattern, into which they cannot quite fit. This results in an especially tight rack, without any possibility of cheating by carefully manipulating the ball positions while racking. This innovative racking technique was invented and patented  as the Rack-M-Rite Racking Template by US professional player David Smith and his partner Dale Craig and first used in professional events on the Billiard Channel Tour in 2000 by tournament director David Vandenburgh. It is now the official rack of the EPBF Euro-Tour.
Another Euro-Tour innovation is a new requirement that the break shot be taken from a "break box", not unlike the "D" break shot zone used in snooker and blackball, consisting of the middle 50% of the "kitchen". This change defeats the common break-from-the-side-rail technique for pocketing the 9 ball on the break and winning the game instantly. While 9 ball breaks are still possible, they are much more difficult under the new rule. This requirement was recently added to the Europe vs. US all-star team event, the Mosconi Cup, but has not otherwise been seen much by North Americans.
Yet a third EPBF change, used on the Euro-Tour for several years, is the "three above the line" rule, a stringent requirement that in order for a break shot to be legal, at least three object balls must either be pocketed or come up-table and cross the head string. Failure to do so constitutes a loss-of-turn (but not ball-in-hand) foul – even if two object balls are pocketed, a potential major windfall for the non-breaking player under these rules. More stringently yet, the requirements are independent – if a ball crosses the head string and is then pocketed, it counts as a pocketed ball but not a head string-crossing ball. This alteration (from WPA's requirement that one object ball be pocketed or four driven to cushions) requires a powerful break shot, and was instituted to thwart a different form of break manipulation, the recently developed "nine-ball soft break", in which a languid break performed correctly, and given a tight rack (such as that produced by EPBF template-trained racking), is almost guaranteed to pocket a wing ball in a foot corner pocket, perhaps even both wing balls, meanwhile the remaining balls stay mostly or entirely on the foot end of the table, giving the breaker an easy run-out of short shots. By effectively banning the soft break, wins "on a silver platter" are much less likely. One problem with this "three above the line" break requirement is that very careful attention must be paid to whether or not particular balls cross the head string, such that even professional referees have had to resort to video playback, as happened several times at the Mosconi Cup, when this rule, too, was introduced in 2007 by the MC's organizers, Matchroom Sport, in an effort to make the event more competitive and interesting to audiences, and more even (the US has mostly dominated the annual event since its inception, and they did in fact lose the 2007 match).
Another Mosconi Cup rule change in 2007 called for racking such that the 9 ball rather than the 1 ball is on the foot spot (i.e. the racker rolls the balls forward farther; the balls remain in the same position in the rack), which further thwarts pocketing a wing ball easily.
Derived games 
Three-ball (historical) 
While the modern folk game of three-ball bears no resemblance to nine-ball, the earliest-known version of three-ball was essentially nine-ball played with only three balls, racked in a triangle,[clarification needed] in which the 3 ball was the money ball. It is a quick game, and (due to the comparatively very high possibility of pocketing the 3 ball on the break) one with a more significant luck component than nine-ball and most other pool games.:254
Six-ball is essentially identical to nine-ball but with three fewer balls, and racked in a three-row triangle, with the 6 ball (or more often the 15 ball; see below) as the money ball, placed in the center of the back row.:224 According to Rudolph "Minnesota Fats" Wanderone, the game arose in early 20th century billiard halls that charged by the rack instead of by the hour, as nine-ball players had already paid for the 10–15 balls and did not want to waste them.:224 This explanation of the game's origin may be particularly plausible because six-ball remains popular today as a diversion or practice round among nine-ball-playing bar pool players, using coin-operated tables that deliver a full set of fifteen balls.
Seven-ball is a similar game, the primary differences being there are only seven object balls, racked in a hexagon, and the game is won by pocketing the 7 ball. Seven-ball is racked with the 1 ball at the apex on the foot spot and the 7 ball (the money ball) in the center of the hexagon. This game is not particularly common, and is primarily known because of ESPN's Sudden Death Seven-ball which aired in the early 2000s. Though hardly necessary, specialized equipment for the game can be purchased, including a unique black-striped seven ball and a hexagonal rack.
Ten-ball is a more stringent variant of the game, using ten balls (racked in a triangle with the 10 ball, the money ball in this case, in the center), and in which the money ball cannot be pocketed early for an early win. Due to its more challenging nature, and the fact that there is no publicly known technique for reliably pocketing specific object balls on the break shot, there have been suggestions among the professional circuit that ten-ball should replace nine-ball as the pro game of choice, especially since the rise of the nine-ball soft break, which is still legal in most international and non-European competition. Regardless of the future of the nine-ball versus ten-ball debate, there are already hotly contested professional ten-ball tournaments.
Carom nine-ball 
Carom nine-ball (also carom nine, for short) is played with the usual nine-ball rack, but breaking with the 1 ball, with the cue ball placed at the head of the rack (in the usual place of the 1 ball). As in regular nine-ball, play progresses from the lowest-numbered ball on the table; however a legal shot is made by shooting the object ball rather than the cue ball. The object ball must make first contact with the cue ball to count as a legal shot, the goal being to carom the object ball into a pocket or into another ball. Once a legal shot has been performed, any ball then sunk counts for that player; the winner is the player to first pocket the nine-ball after a legal shot.
3-6-9 nine-ball 
A gambling version of nine-ball played with group of people. The game is played like regular 9 ball with a player order. Heckling the shooters is allowed but no touching may occur. Money balls are the three, six, and nine ball. Values of the money balls are 1-1-2 where each player pays out to the person who sunk a money ball. If the nine ball is sunk, the payout is the nine ball value and what ever money balls are left on the table. If a money ball is pocketed and the cue ball is scratched, that player must pay out that value to each of his opponents. Winner of the game has break on the next game, player before winner racks the next game.
See also 
- Billiards: The Official Rules and Records Book (50th Anniversary Commemorative edition ed.). Coralville, IA: Billiard Congress of America (BCA). 1998. p. 26.
- Jewett, Bob (February 2008). "Killing Me Softly?: The Outbreak of the Soft Break Threatens the Game of 9-ball". Billiards Digest 30 (3) (Chicago, IL, US: Luby Publishing). pp. pp. 34–35. ISSN 0164-761X.
- Panozzo, Mike (February 2008). "Long Live the Cup!". Billiards Digest 30 (3) (Chicago, IL, US: Luby Publishing). pp. pp. 34–35. ISSN 0164-761X.
- Shamos, Mike (1999). The New Illustrated Encyclopedia of Billiards. New York City, NY, US: Lyons Press. ISBN 1-55821-797-5
- WPA/BCA World Standardized Rules for nine-ball
- Pro9 — website detailing the many nine-ball tournaments held within the British Isles and beyond.
- Historical nine-ball and ten-ball match videos by year