Understanding Curling

Here’s a guide to the game

General
Playing surface
Players
Team naming
Equipment
Game play
Throwing
Delivering the rock
Sweeping
Free guard zone
Last rock (the "Hammer")
Scoring
Conceding a game
Dispute resolution
Strategy

General
Curling is a team sport with similarities to bowls and shuffleboard, played by two teams of four players each on a rectangular sheet of carefully prepared ice.

Teams take turns sliding heavy, polished granite stones down the ice towards the target (called the house).

Two sweepers with brooms accompany each rock and use timing equipment and their best judgment, along with direction from their teammates, to help direct the stones to their resting place.

The complex nature of stone placement and shot selection has led some to refer to curling as "chess on ice."
Playing surface
The curling sheet, is an area of ice 45 to 46m in length by 4.4 to 5.0m in width, carefully prepared to be as close to level as possible.

The ice is most often frozen by means of a refrigeration plant that cools a brine solution running lengthwise in numerous pipes under the curling sheet. A key part of the preparation of the playing surface is the spraying of water droplets, called "pebble," onto the level ice. Due to the friction between the stone and pebble, the stone turns to the inside or outside, causing the stone to "curl." The amount of curl can change during a game as the pebble wears. The surface of the ice is maintained at a temperature around 5°C.

Making and maintaining perfect ice conditions at a curling club is as much art as science. Most curling clubs have an ice maker, whose main job is to care for the ice. At the major curling championships, ice maintenance is extremely important.

Large events, such as the Brier or other national championships, are typically held in an arena that presents a challenge to the ice maker, as they must constantly monitor and adjust the ice and air temperatures as well as air humidity levels to ensure a consistent playing surface. It is common for each sheet of ice to have multiple sensors embedded in order to monitor surface temperature, as well as probes set up in the seating area (to monitor humidity) and in the compressor room (to monitor brine supply and return temperatures).

On the sheet, a 3.7m wide set of concentric rings, called the house, is painted near each end of the rink. The centre of the house, known as the button, is marked by the junction of two lines that divide the house into quarters. The two lines are the centre line, which is drawn lengthwise down the centre of the sheet, and the tee line, drawn 4.9m from the backboard and parallel to it. Two other lines (the hog lines) are drawn parallel to each backboard and 11m from them.

The rings that surround the button are defined by their diameter as the four-foot, eight-foot, and twelve-foot rings. They are usually distinguished by colour. The inner rings are merely a visual aid for judging which stone is closer to the centre; they do not affect scoring. However, a stone that is not at least touching the outside of the 3.7m ring (i.e., more than 1.8m from the centre) is not in the house and therefore does not score.

Located twelve feet behind the button are the "hacks." A hack is a device used to provide traction to the curler making a shot; the curler places the foot he or she will push off with in the hack. On indoor rinks, there are usually two fixed hacks (rubber-lined holes) one on each side of the centre line, with the inside edge no more than 76mm from the centre line and the front edge on the hack line. A single moveable hack may also be used.
Players
Curling is played between two teams of four curlers each, with team members named for the usual order in which they play. The lead plays first, then the second, the third (or mate or vice), and finally the fourth. The fourth is typically the skip (team captain), but not always.

Lead
The lead, or first, throws the team's first two stones of an end (round of play), and sweeps for the other team members. Strategically, the lead usually has similar shots from end to end, usually throwing guards or draws. The placement of the lead's rocks will usually dictate how the strategy for the end sets up.

Second
The second throws the team's 3rd and 4th stones and sweeps for all other players. The second's role when shooting is often to remove opposition stones in front of the house, as his or her shots are the first rocks thrown after the end of the free guard zone.

Third
Also called the vice skip, vice, or mate, the third throws the team's 5th and 6th stones and usually sweeps for the second and the lead. The third usually assists the skip in his or her duties. When it is the skip's turn to throw, it is usually the third who holds the broom for the skip.

After each end, the thirds for both teams must reach an agreement as to which team scored and with how many points. If there is a disagreement or uncertainty, the thirds will call an official to see which ones are closer. If no officials are present, the thirds will measure themselves; at this time, only the thirds are allowed in the house. In major tournaments, the scorekeeping is left to an official. Depending on the tradition, when the third's team scores, the third will record it on the scoreboard.

Depending on the tradition, the third may flip a coin, with the opposing third to determine who will have last-rock (hammer) advantage at the beginning of a game. The winner of the toss has the option to pick either last rock or the colour of the rocks they wish to play with. In major tournaments, these decisions are usually made beforehand.

Skip
The skip is the captain of the team, and he or she determines strategy. Based on such strategy, the skip holds the broom indicating where the player throwing must aim (calling the shot).

When it is the skip's turn to throw, the vice skip (usually the third) holds the broom. The skip usually throws the last two rocks of the end; however, some teams have the skip throwing in other positions.

The skip rarely does any sweeping, except in the house and behind the tee line. The skip is required to stay out of the playing area when it is the other team's turn, but he or she is allowed to sweep stones in motion behind the tee line as a result of their shot.

In international rules, the player in charge of the house is the only player allowed to sweep their opponent's stones behind the tee line. For most of the end, that's the skip; but when the skip is throwing, the vice skip takes charge of the house.

Fourth
The fourth refers to the thrower of the last two stones in each end for a team if that player is not the skip. That is, if the skip does not play last rocks in each end, the last player to throw is known as the fourth.
Team naming
A team will usually be identified by the last name of the skip, unless they are representing in the World Championships or the Olympics, in which case they would be known as "Team (country)."
Equipment
Shoes
The slider shoe (center)with its thin Teflon surface, is worn during delivery to slide on the ice; a slip-on gripper (left) is worn over the slider at other times. The other shoe (right) has a rough surface to give its wearer traction on the ice.

Casual players may wear running shoes and improvise a slider by applying electrical tape (or something similar) to their off foot.

Higher-end shoes are often made of leather, while lower-end shoes are often made of vinyl.

Broom (brush)
The curling broom is used to sweep the ice surface in front of the rock. Aggressive sweeping momentarily melts the ice, which lessens friction, thereby lessening the rock's deceleration while straightening its trajectory.

The broom can also be used to clean debris off the ice, which is important to keep a throw from "picking".

The skip will also hold a broom at the end of the rink opposite from the delivering player as a target for the deliverer to aim the rock toward.

In earlier days, brooms were made of corn strands and were similar to household brooms. Brushes were used primarily by elderly curlers as a substitute for corn brooms. Today, brushes have replaced traditional corn brooms at every level of curling, but are universally referred to as brooms. Curling brushes may have fabric, hog hair, or horsehair heads. Most top quality modern broomsticks are now made of materials such as carbon fibre, allowing faster sweeping; lower-end brooms are often made of fibreglass.

Brooms are also used by most curlers as a balancing aid during delivery of the stone.

Curling stone (rock)
The curling stone is circular in shape and weighs between 17- 20kg with a handle and bolt attached. The stone has a maximum allowable circumference of 910mm. A stone must be a minimum of 110mm in height.

The handle is attached to the stone by means of a bolt that runs vertically through a hole in the centre of the stone. The handle allows the rock to be gripped and rotated upon release.

When the rock is thrown with the right hand, clockwise rotation is referred to as an in-turn; counter clockwise rotation is referred to as an out-turn. The opposites are true if the rock is thrown with the left hand. The handles are coloured to differentiate the rocks belonging to each team. Two popular colours in major tournaments are red and yellow. The handle may be of the "eye on the hog" variety for detecting hog line violations.

The top and bottom of a curling stone are concave. The surface in contact with the ice, known as the running surface, is a circle 6.3 - 13mm thick. This narrow running surface is where the ice and the stone interact. On properly prepared ice, the rock's path will bend (curl) in the direction the front edge of the rock is turning, especially toward the end of its motion. The degree of curl depends on several factors, including the preparation of the ice and the flattening of common paths to the house during the game. Ice on which the rocks curl well is said to be "swingy."

The Scots, in particular, believe that the best-quality curling stones are made from a specific type of granite called "ailsite," found on the Ailsa Craig, an island off the Ayrshire coast. According to the Scottish Curling Stone Company, Ailsite has very low water absorption, which prevents the action of freezing and melting water from eroding the stone. In the past, most curling stones were made from this granite. However, the island is now a wildlife reserve and is no longer used for quarrying. Because of the particular rarity of Ailsite, costs for curling stones can reach as much as US$1,500 for the best stones.

Many curling clubs use a lower-grade stone that can cost upwards of US$500. There are also stones that use a disc with a running surface of Ailsite attached below another type of granite. Very informal neighbourhood curling clubs with limited resources may make cylindrical "curling stones" out of concrete-filled cans or bowls.

Other equipment
Curling pants are made to be stretchy in order to accommodate the curling delivery.

Curlers may also wish to use a stopwatch to time the rocks whilst sweeping to get a feel of how fast the rock is going; stopwatches can be attached either to a piece of clothing or the broom itself.

There is also a wide variety of curling gloves and mittens, which are used to both keep the hands warm (if necessary) and for better traction on the broom.

Specialized equipment
A special handle for stones, called "Eye on the Hog," which integrates electronics to ensure the stone is released before it crosses the hog line, has recently been developed. The handle is coated in metallic paint; the circuitry detects the relative charge of the thrower's hand contact to determine if they are still in contact, and a linear field is established at the hog line to indicate its location to the internal sensor. Lights at the base of the handle indicate whether contact was sustained past the line. Not only does this remove the chance of human error (eliminating the game's most frequent cause of controversy), but it means there is no need for hog line officials as well.

Although the rock is designed to be delivered by players grasping the handle as they slide down the ice, a special "delivery stick" may be used by players incapable of delivering the rock in this fashion. Such a stick is designed to attach to the handle so that it can be released without requiring the player to place a hand on the handle in a crouched position. This allows the game to be played by players with disabilities as well as by those unable to crouch comfortably.
Game play
A competitive game usually consists of ten ends. Recreational games are most commonly eight ends.

An end consists of each player from both teams throwing two rocks down the sheet with the players on each side alternating shots, for a total of sixteen rocks.

If the teams are tied at the completion of ten ends, an extra end is played to break the tie. If the match is still tied after the extra end, play continues for as many ends as may be required to break the tie.

The winner is the team with the highest score after all ends have been completed.

It is not uncommon at any level for a losing team to terminate the match before all ends are completed if it believes it no longer has a realistic chance of winning. Playoff games at national and world championships require eight ends to be completed before allowing a losing team to concede in this manner. Competitive games will usually end once the losing team has “run out of rocks”, that is, once it has fewer stones in play and/or available for play than the number of points needed to tie the game in the final end.

In international competition, each side is given 73 minutes to complete all of their throws. Each team is also allowed two 60-second timeouts per ten-end game. If extra ends are required, each team is allowed ten minutes of playing time to complete their throws and one added 60-second timeout for each extra end.
Throwing
When throwing the rock, the player must release it before reaching the near hog line (players usually slide while releasing their shots) and it must completely cross the far hog line; otherwise, the rock is removed from play (hogged).

An exception is made if the thrown stone fails to cross the far hog line after striking a resting stone in play (e.g., a stone just past the hog line). In that case, the thrown stone will legally remain in play.

The rule concerning releasing the rock before the hog line is rarely enforced in club play, unless abuse of the rule occurs. In major tournaments, the "eye on the hog" sensor in the rock will indicate whether the rock has been legally thrown or not. If the lights on the rock turn red, the rock will be immediately pulled from play instead of waiting for the rock to come to rest.

While the first three players throw their rocks, the skip remains at the far end of the ice to guide the players. While the skip is throwing, the third takes this role. Thus, each time a rock is thrown, there is one player throwing the rock and another player at the far end. The other two players may choose to sweep in front of the rock.
Delivering the rock
While not compulsory, most curlers deliver the rock from sliding out from the hack. When sliding out, one shoe (the one with the non-slippery sole) is positioned against one of the hacks (a position referred to as being in the hacks). For a right-handed curler, this means starting from the left hack, and vice versa for a left-handed curler.

When delivering the rock, it is important to remember that the momentum behind how much weight is applied to the rock depends on how much leg drive the delivery has. It is usually not wise to push the rock with the arm unless absolutely necessary.

When in the hack, one must crouch down with the body lined up and shoulders square with the skip's broom at the other end. While in the hack, one may hold a broom out for balance. Different curlers hold their broom out in many different fashions. The broom is held in the hand opposite from the rock and should be positioned so that the non-sweeping side of the broom is against the ice. This prevents drag caused by the soft head of the broom dragging against the ice.

Before any delivery, it is important to ensure that the running surface of the rock is clean and that the area around you is clean as well. This is achieved by wiping the running surface of the rock with either your hand or with the broom and then cleaning the area around you with the broom. The reason for this is that any dirt in the area or on the bottom of a rock could alter the trajectory of it and ruin the shot. When this happens, it is called a "pick."

After cleaning the rock, the next step is to know what rotation, or turn, to put on the rock. The skip will usually tell the thrower this information. The thrower will then place the handle of the rock generally at either a "two o'clock" or a "ten o'clock" position. When delivering the rock, the thrower will turn the rock from one of these two positions toward the "twelve o'clock" position before releasing it. A rock turned from ten o'clock to twelve will spin clockwise and curl to the right, and a rock turned from two o'clock to twelve will have the opposite effect. A generally desired rate of turn is about two and a half rotations before coming to a rest.

Once the thrower knows the turn to give the rock, the thrower will place the rock in front of his or her toe in the hack. At this point, the thrower will then start his or her delivery. This begins by slightly rising from the hack and moving the rock back to one's toe. This is the beginning of a pendulum movement that will determine the force given to the rock. Some older curlers will actually raise the rock in this backward movement, as this is what they are accustomed to.

The forward thrust of the delivery comes next. The thrower moves his or her slider foot in front of the other foot while keeping the rock ahead of him. The thrower then lunges out from the hack. The more thrust from this lunge, the more power or "weight" the rock will have. When lunging out, the gripper foot will drag behind the thrower. When lunging out, it is important to push as precisely as possible in the direction of the skip's broom at the other end, so that the "line" of the rock is accurate. The rock should be released before the thrower's momentum wanes, at which point the thrower imparts the appropriate curl, keeping in mind the stone should be released before the first hog line.

The amount of weight given to the rock will also be told to the thrower by the skip at the other end. This usually occurs by the skip's tapping the ice with his broom where he or she wants the rock to be delivered. In the case of a take-out or a tap, the skip will tap the rock that he or she wants removed or tapped. Generally, the skip will not hold the broom in the same place he expects the rock to stop or hit; instead, the skip estimates how much the rock will curl as it travels down the ice and holds the broom where he believes the thrower will have to aim in order to hit the target.
Sweeping
When a rock is delivered, it is important that there be two players following the rock so that they are ready to sweep its path if needed. Sweeping is done for two reasons: to make the rock travel farther, and to make the rock travel straighter (curl less). When sweeping, pressure and speed of the brush head are key in slightly melting the pebbled ice in the path of the rock.

One of the interesting strategy aspects of curling is knowing when to sweep. When swept, a rock will usually travel both farther and straighter. In some situations, one of the two is often not desirable (for example, a rock may have too much weight, but needs sweeping to prevent curling into a guard), and the team must decide which is better: getting by the guard but travelling too far or hitting the guard.

Much of the yelling that goes on during a curling game is the skip calling the line of the shot. The skip evaluates the path of the rock and calls to the sweepers to sweep as necessary to hold the rock straight. The sweepers themselves are responsible for judging the weight of the rock and ensuring the length of travel is correct. Simultaneously, the sweepers must communicate the weight (speed) of the rock back to the skip.

Some teams use stopwatch timing, from back line to the nearest hog line as a sweeping aid. Many teams use the "Number System," where the playable area is divided into ten zones, each assigned a number, and these numbers are used to communicate where the sweepers estimate the rock will stop.

Usually, the two sweepers will be on opposite sides of the rock's path, although depending on which side people's strengths are, this may not always be the case. Speed and pressure are vital to sweeping. In gripping the broom, one hand should be one third of the way from the top (non-brush end) of the handle while the other hand should be one third of the way from the head of the broom. The angle of the broom to the ice should be so that the most force possible can be exerted on the ice. The precise amount of pressure may vary from relatively light brushing "just cleaning" (to ensure debris is not in the way) to maximum-pressure scrubbing.

Sweeping can be done anywhere on the ice up to the "tee line," as long as it is only for your own team's rock. Once your team's rock crosses the tee line, only one player may sweep it. Additionally, when an opposing rock crosses the tee line, one player from your team is allowed to sweep it. This is the only case that a rock may be swept by an opposing team member. In international rules, this player must be the skip; or if the skip is throwing, then the third.
Touched stones
Occasionally, players may accidentally touch a stone with their broom or a part of their body. This is often referred to as "burning" a stone. When a player touches a stone, s/he is expected to call themselves on it.

The result of a touched stone varies based on which team touched the stone; whether the stone was being delivered, stationary, or set in motion by another stone; and whether touching the stone impacted the positions of other stones. Rules also vary across different governing bodies.
Types of shots
Essentially, there are three kinds of shots in curling, the guard, the draw and the takeout; there are many variations of these shots, however.

Guards are shots thrown infront of the house, usually to guard shot-rock (rock closest to the button at a certain time) or to make the opposing team's shot difficult.

Draws are shots in which the stone is thrown only to reach the house, while takeouts are shots designed to remove stones from play.

Choosing which shot to play will determine whether the thrower will use an in-turn or out-turn—for a right-handed person, the clockwise and counter-clockwise rotation of the stone, respectively.

Possible guard shots include centre-guard and corner-guards (left and right sides of the centre line). Draw shots include raise (and angle-raise), come-around, and freeze, and takeout shots include peel, hit-and-roll and double.
Free guard zone
Until four rocks have been played (two from each side), rocks in the free guard zone (those rocks left in the area between the hog and tee lines, excluding the house) may not be removed by an opponent's stone. These are known as guard rocks. If the guard rocks are removed, they are replaced to where they were before the shot was thrown, and the opponent's rock is removed from play and cannot be replayed. This rule is known as the four-rock rule or the free guard zone rule.

The three-rock rule, known as the Modified Moncton Rule, this rule, a relatively recent addition to curling, was added in response to a strategy of "peeling" opponents' guard stones (knocking them out of play at an angle that caused the shooter's stone to also roll out of play, leaving no stones on the ice). A team in the lead would often employ this strategy during the game. By knocking all stones out, the opponents could at best score one point (if they had the hammer). Alternatively, the team with the hammer could peel rock after rock, which would blank the end, keeping the last rock advantage for another end. While a sound strategy, this made for an unexciting game.

One strategy that has been developed by curlers in response to the free guard zone is the "tick" game, where a shot is made attempting to knock (tick) the guard to the side, far enough that it is difficult or impossible to use but still remaining in play while the shot itself goes out of play. The effect is functionally identically to peeling the guard but significantly harder, as a shot that hits the guard too hard (knocking it out of play) results in its being replaced, while not hitting it hard enough can result in its still being tactically useful for the opposition. There's also a greater chance of the shot missing the guard entirely due to the greater accuracy required to make the shot. Due to the difficulty of making this type of shot, only the best teams will normally attempt it, and it does not dominate the game the way the peel formerly did.
Last rock (the "Hammer")
Last rock advantage in an end is called the hammer.

Before the game, teams typically decide who gets the hammer in the first end by coin toss or similar method. In all subsequent ends, the hammer belongs to the team that did not score in the preceding end. In the event that neither team scores, the hammer remains with the same team.

Naturally, it is easier to score points with the hammer than without; in tournament play, the team with the hammer generally tries to score two or more points. If only one point is possible, the skip will often try to avoid scoring at all in order to retain the hammer until the next end, when two or more points may be possible. This is called a blank end. Scoring without the hammer is commonly referred to as stealing, or a steal, and is much more difficult.
Scoring
After both teams have delivered eight rocks, the team with the rock closest to the button is awarded one point for each of its own rocks that is closer than the opponent's closest rock.

Rocks that are not in the house (further from the centre than the outer edge of the 3.7m ring) do not score even if no opponent's rock is closer. A rock is considered in the house if any portion of its edge is over any portion of the 3.7m ring. Since the bottom of the rock is rounded, a rock just barely in the house will not have any actual contact with the ring, which will pass under the rounded edge of the stone, but it still counts. This type of rock is known as a "biter."

The score is marked on a scoreboard, of which there are two types. One is the baseball-type scoreboard, which is usually used for televised games. On this scoreboard, the ends are marked by columns 1 through 10 (or 11 for the possibility of an extra end to break ties) plus an additional column for the total. Below this are two rows, one for each team. The number of points each team gets in an end is marked this way.

The other form of scoreboard is the one used in most curling clubs. It is set up in the same way, except the numbered row indicates a team's progress in scoring points rather than marking ends, and it can be found between the rows for the teams. The numbers placed are indicative of the end. If the red team scores three points in the first end (called a three-ender), then a 1 (indicating the first end) is placed beside the number 3 in the red row. If they score two more in the second end, then a 2 will be placed beside the 5 in the red row, indicating that the red team has five points in total (3+2). This scoreboard works because only one team can get points in an end. However, some confusion can exist if no team gets points in an end. This is called a blank end, and the end number usually goes in the farthest column on the right in the row of the team that has the hammer (last rock advantage), or on a special spot for blank ends.
Conceding a game
When a team feels it is impossible or near impossible to win a game, they will usually shake hands with the opposing team to concede defeat. This may occur at any point during the game, but usually happens near the final end. When a game is completed by playing all ends, both teams also shake hands. Hands are also shaken before the game, accompanied by saying "Good curling!" to the opposing team.

Unlike other sports, there is no negative connotation associated with conceding in curling. In fact, in many competitions, a team is required to concede when it is mathematically impossible for them to tie a game. In more social situations, it is often considered a breach of etiquette (or at least looked down upon) to keep playing when the game is well out of reach.
Dispute resolution
Most decisions about rules are left to the skips, although in official tournaments, decisions may be left to the officials. However, all scoring disputes are handled by the third, or vice skip.

No players other than the third from each team should be in the house while score is being determined. In tournament play, the most frequent circumstance in which a decision has to be made by someone other than the third is the failure of the thirds to agree on which rock is closest to the button. An independent official then measures the distances using a specially designed device that pivots at the centre of the button. When no independent officials are available, the thirds measure the distances.
Strategy
Strategy in an end of curling depends on the circumstances. It depends on the team's skill, the opponent's skill, the conditions of the ice, the score of the game, how many ends remain, and whether the team has last rock advantage.

 A team may play an end aggressively; that is, to have a lot of rocks in play by throwing mostly draws. This makes for an exciting game, but is very risky. However, the reward can be very great. A team may also wish to play an end defensively. This means throwing a lot of hits preventing a lot of rocks in play. This is generally considered to be less exciting, and is less risky. A good drawing team will usually opt to play aggressively, while a good hitting team will opt to play defensively.

If a team does not have the hammer in an end, they will opt to try and clog up the four-foot (the four-foot wide area surrounding the centre line) so as to prevent the opposing team from accessing the button. This can be done by throwing "centre line" guards (rocks in front of the house touching the centre line). These can be tapped into the house later or drawn around. If a team has hammer, they want to keep this four-foot zone free of rocks so that they have access to the button area at all times. A team with hammer may throw up a "corner guard" as their first rock of an end to utilize the free guard zone. A corner guard is a rock in front of the house that is not in the four-foot zone. Corner guards are key for a team to score two points in an end, because they can either draw around it later or hit and roll behind it, making the opposing team's shot to remove it more difficult.

Ideally, the strategy in an end for a team with hammer is to score two points or more. Scoring one point is often a wasted opportunity, as they will then lose last-rock advantage for the next end. If a team can't score two points, they will often attempt to "blank an end" by removing any leftover opposition rocks and rolling out; or, if there are no opposition rocks, just throwing the rock through the house so that no team scores any points, and the team with the hammer can try again the next end to score two or more with it. Generally, a team without hammer would want to either force the team with hammer to only one point (so that they can get hammer back) or "steal" the end by scoring one or more points of their own.