Tennis is played on a rectangular, flat surface, usually grass, clay, a hardcourt of concrete and/or asphalt and occasionally carpet (indoor). The court is 78 feet (23.77 m) long, and 27 feet (8.23 m) wide for singles matches and 36 ft (10.97 m) for doubles matches.[37] Additional clear space around the court is required in order for players to reach overrun balls. A net is stretched across the full width of the court, parallel with the baselines, dividing it into two equal ends. The net is 3 feet 6 inches (1.07 m) high at the posts and 3 feet (91.4 cm) high in the center.[37] The modern tennis court owes its design to Major Walter Clopton Wingfield who, in 1873, patented a court much the same as the current one for his sticke tennis (sphairistike). This template was modified in 1875 to the court design that exists today, with markings similar to Wingfield's version, but with the hourglass shape of his court changed to a rectangle.[38] Lines The lines that delineate the width of the court are called the baseline (farthest back) and the service line (middle of the court). The short mark in the center of each baseline is referred to as either the hash mark or the center mark. The outermost lines that make up the length are called the doubles sidelines. These are the boundaries used when doubles is being played. The lines to the inside of the doubles sidelines are the singles sidelines and are used as boundaries in singles play. The area between a doubles sideline and the nearest singles sideline is called the doubles alley, which is considered playable in doubles play. The line that runs across the center of a player's side of the court is called the service line because the serve must be delivered into the area between the service line and the net on the receiving side. Despite its name, this is not where a player legally stands when making a serve.[39] The line dividing the service line in two is called the center line or center service line. The boxes this center line creates are called the service boxes; depending on a player's position, he or she will have to hit the ball into one of these when serving.[40] A ball is out only if none of it has hit the line or the area inside the lines upon its first bounce. All the lines are required to be between 1 and 2 inches (51 mm) in width. The baseline can be up to 4 inches (100 mm) wide.[39] Play of a single point Main article: Point (tennis) The players (or teams) start on opposite sides of the net. One player is designated the server, and the opposing player is the receiver. The choice to be server or receiver in the first game and the choice of ends is decided by a toss before the warm-up starts. Service alternates game by game between the two players (or teams.) For each point, the server starts behind the baseline, between the center mark and the sideline. The receiver may start anywhere on their side of the net. When the receiver is ready, the server will serve, although the receiver must play to the pace of the server. In a legal service, the ball travels over the net (without touching it) and into the diagonally opposite service box. If the ball hits the net but lands in the service box, this is a let or net service, which is void, and the server retakes that serve. The player can serve any number of let services in a point and they are always treated as voids and not as faults. A fault is a serve that falls long or wide of the service box, or does not clear the net. There is also a "foot fault", which occurs when a player's foot touches the baseline or an extension of the center mark before the ball is hit. If the second service is also a fault, the server double faults, and the receiver wins the point. However, if the serve is in, it is considered a legal service. A legal service starts a rally, in which the players alternate hitting the ball across the net. A legal return consists of the player or team hitting the ball before it has bounced twice or hit any fixtures except the net, provided that it still falls in the server's court. A player or team cannot hit the ball twice in a row. The ball must travel past the net into the other players' court. A ball that hits the net during a rally is still considered a legal return. The first player or team to fail to make a legal return loses the point. The server then moves to the other side of the service line at the start of a new point