Racquetball is, as the name suggests, a racquet-and-ball sport played in an enclosed area by two players or pairs.
A regulation racquetball court is 40 feet long, 20 feet wide and 20 feet high; indoor courts typically have walls and ceiling faced with a durable smooth sheetrock, sometimes with a glass rear wall and/or a railing in the upper rear section of the court for spectator viewing, painted white with a light-colored wooden floor. Outdoor courts are most often formed from poured concrete slabs on all sides with no ceiling (or only a partial ceiling).
On the floor, three lines parallel to the front wall are painted in red, at 15, 20 and 25 feet from the front wall. The closest line at 15 feet is known as the "service line", while the line at 20 feet is the "short line". These two lines are solid, and form the "service area" within which the serving player must stand while serving the ball. Within the service area are four additional lines parallel to the side walls, at 18 and 36 inches from each wall. The 18" lines, with the short and service lines and the side wall, define the "doubles boxes"; the non-serving player of the serving pair must stand in one of these boxes while his partner serves the ball. The 36" lines are the "screen lines"; generally the serving player must stay to the inside of each of these lines, toward the center of the service area, especially when making certain kinds of banking serves. Behind the short line is the "receiving line" at 25 feet from the front wall; this is typically a dashed line that marks the point at which the receiving player or pair may play the ball if it has not yet bounced after contact.
The ball used is a smooth hollow rubber ball 2.25 inches in diameter. The most common color for indoor play is blue, though racquetballs are made in a variety of colors often with accompanying small changes to the ball's materials, bounce or spin characteristics, meant for a variety of playing styles or environments (a tougher rubber, for instance, can be used when playing in a court with rough wall or floor surfaces). The racquet is a tensioned polymer net in an aluminum frame, similar in form and construction to a tennis racquet but slightly smaller and lighter, with a maximum length from pommel to far edge of 22". Players typically wear polo shirts or T-shirts and gym or basketball shorts while playing, and many players often additionally wear some protective clothing to guard against hits by the ball or collisions with another player; athletic cups, kneepads, and safety goggles are common, with goggles being required in competition play.
Play of a rally starts with a serve; one player stands within the "service zone", bounces the ball once off the floor, and then hits it with his racquet so that it bounces off the front wall, does not contact the ceiling or more than one other wall, and then bounces off the floor beyond the "short line" but before contacting the back wall. A serve that does not meet all these conditions is a "fault"; most recreational play allows the player a second serve attempt if they commit a fault, and on the second fault a point is awarded to the opponent, though in higher competition levels a "one-serve rule" is usually in place where any fault results in a point to the opponent.
Once the ball has bounced off the floor behind the short line, or has passed the receiving line and the opposing player thinks it will hit the floor before the back wall, the receiving player may play the ball by hitting it off of his racquet. To be a legal hit, after leaving the player's racquet the ball must contact the front wall before bouncing off the ground. The opposing player must then hit it off his own racquet before it bounces on the floor twice (he may allow it to bounce off the floor once or may hit it "on the fly" without letting it bounce at all). Players (or pairs in doubles) then take turns hitting the ball until one player does not make a legal hit, either letting the ball bounce twice, or hitting it in such a way that the ball hits the ground before the front wall.
Racquetball is unique among racquet sports in that all surfaces enclosing the court are "in play" during normal play of a rally, with no "out of bounds" unless the court is not fully enclosed (in which case a hit that causes the ball to leave the playing area is not legal and the player who last hit loses the point). After the serve, as long as the rules of a legal hit are followed, the players may hit the ball into or allow it to bounce off of any portion of not only the front wall and floor, but the side and rear walls and the ceiling (if it exists). This play dynamic is most similar to squash, but that game has lines marking valid areas of the front and side walls that can be played off of, and the rear wall is out of play. Some recreational court operators may institute a local rule that the ceiling is out of play to discourage hitting into it, as it may be constructed of a less durable material such as drop ceiling tiles, or it may have ventilation or lighting equipment protruding from its face which can cause the ball to bounce off in unpredictable ways. However, competition-level courts must allow the ceiling to be played off of either directly or indirectly.
Once a player fails to make a legal hit, the other player or pair wins the rally. If that side served, they win a point; if the non-serving side wins the rally, they do not get a point but are awarded the serve. This is similar to the original scoring rules for volleyball, however most volleyball competitions now award a point on each rally won. The same "point on every rally" variation can be used in recreational play to speed up the game, but all sanctioned competitions still use the "must serve to score" format.
A game is typically played to 15 points. The U.S. competitive match format is a best-of-three game series, with the third game if necessary being played to only 11 points, and unlike most other racquet sports the winner of any game is not required to win by two. Canadian rules are the same except that the two-point winning margin is required. Most other matches run under International Racquetball Federation rules are the same as the U.S., however top-level professional competitions are often best-of-five matches with all games played to 11, and requiring a two-point winning margin.
Racquetball is typically played by adults in recreational settings for fun and exercise. There is no official minimum age to play in most jurisdictions, but unlike field sports the dimensions of the court cannot be easily changed, so a younger player must have the strength and coordination to be able to play on the full-size adult court, so instruction in racquetball often doesn't begin until age 7 unlike other sports where children can begin to learn to play at three or four. Levels of competition range from casual recreational play between friends up to international professional tournaments, including the U.S. Racquetball Open, the World Racquetball Championship and events at the Pan-American Games.