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Curling 101: Rules

Feb 26, 2010; Vancouver, BC, CANADA; China verses Switzerland during the womens curling bronze medal match held at Vancouver Olympic Centre during the 2010 Vancouver Winter Olympics.
Feb 26, 2010; Vancouver, BC, CANADA; China verses Switzerland during the womens curling bronze medal match held at Vancouver Olympic Centre during the 2010 Vancouver Winter Olympics.

Events

There are three curling events: the men’s tournament and the women’s tournament, which are identical in format, and mixed doubles. A men’s tournament was contested at the inaugural Olympic Winter Games in 1924, but the IOC did not officially recognize the results of that tournament until 2006. The men’s tournament returned to the Olympic program at the 1998 Nagano Games, while the women’s event appeared for the first time in 1998. Mixed doubles curling made its Olympic debut in 2018.

Competition Rules

The Game

The men's and women's tournaments are a competition between two teams with four players each. Mixed doubles is played by two players. One man and one woman on each team. 

The game is played on ice and the two teams take turns pushing 42-pound stones towards a series of concentric circles. The object is to get the stones as close to the center of the circles as possible. The center of the circles is known as the tee, which can also be referred to as the “button.” A team scores a point for each stone that is closer to the button than the opponents’ best stone, provided that the stone is within 6 feet (1.83 meters) of the tee. This circular area is known as the house; it is the scoring zone in curling.
    
Games in the men's and women's tournaments consist of 10 ends. Mixed doubles play eight ends (An end is similar to a baseball inning.) During each end of traditional curling, each team delivers eight stones, two stones per person. Mixed doubles teams play five stones each and start every end with one stone that has been pre-placed, so the maximum amount of points in each end is six.

Men's and women's teams deliver the stones in a set order, which is presented to the officials before the game. The first player is known as the lead, he or she is followed by the second, then the third (who is often called the vice-skip) and finally the skip, who is the leader of the team. Each end starts with the leads alternating throws until they have each thrown their two stones. They are followed by the seconds in the same manner, and so on. The order of the lineup may not be changed during the game. In mixed, one player delivers stones one and five. The other player delivers stones two, three and four. Both players are allowed to switch playing positions in-between ends.

The score for the end is determined when all stones have been delivered. The team that scores points in an end shoots first in the next end. The team that does not score shoots last. Shooting last is described as “having the hammer.” If neither team scores, the team that shot last in the end, shoots last again in the next end.

The team with the most points at the conclusion of all ends is the winner.

During the round robin, a team may concede the game once a minimum of six ends have been completed. During the playoffs, a minimum of eight ends must be completed. Conceding the game when the losing skip feels he is too far down to come back is fairly common and is an accepted part of the etiquette of the sport. It should happen multiple times during the course of the Olympics.

If the game is tied at the conclusion of regulation, extra end(s) is played. Whichever team scores first is the winner.

The Playing Surface
    
The playing surface in curling is 150 feet (45.72 meters) long and 16 feet, 5 inches (5 meters) wide. The ice is set up to accommodate play in both directions, meaning the surface is symmetrical with a house at each end. The house is four concentric circles, with the outer edge of the outer circle having a radius of 6 feet, the next circle a radius of 4 feet, the next circle a radius of 2 feet, and the innermost circle having a minimum radius of 6 inches. This outside circle marks the edge of the house.

Players start a stone moving from a rubber block called the hack. Players push off from the back and begin sliding forward, guiding the stone along the ice. Players must release the stone before the front edge touches the hog line, which is 33 feet from the hack and 93 feet from the tee line at the other end. 

At the rear edge of each house is the back line.  It is located 6 feet from the tee line.

Free Guard Zone
    
The area between the hog line and the tee line, excluding the house, is known as the Free Guard Zone. No stone in this area may be removed from play by the opposition until the first four stones in an end have come to rest. Players are allowed to bump other stones with shots, but are not allowed to knock a stone out of play. 

Any shot played when the Free Guard Zone rule is in effect that results in an opposition stone being knocked out of play is an infraction. In this case the played stone is removed from play and any other stone that was moved is replaced. For any stone lying within the house, normal rules apply at all times.
    
This rule was enacted in 1991 to hinder defense-oriented play. In the past, teams would knock out one another’s rocks repeatedly resulting in low scoring games that were boring to many spectators.

Positioned stones (Mixed Doubles only)

Before the start of every end, one team shall place their team’s “positioned” stone at the playing end of the sheet in one of two positions, designated A, and the opponent’s “positioned” stone shall then be placed in whichever position (A or B) remains vacant. The location of these positions shall be as follows:

(a) Position A: Placement so that the stone is bisected by the center line and is either immediately in front of or immediately behind one of 3 points in the ice. The points are placed on the center line:

(i) at the mid-point between the hog line and the outermost edge of the top of the house, or

(ii) 0.915 m. (3 feet) from the mid-point closer to the house, or

(iii) 0.915 m. (3 feet) from the mid-point closer to the hog line.

Based on the ice conditions, the Chief Umpire shall determine the specific placement for Position A to be used before the start of the pre-game practice and that same placement must be used for the entire game.

(b) Position B: Placement so that the stone is bisected by the center line and is in the back of the 4-foot circle. The back edge of the stone is aligned with the back edge of the 4-foot circle.

Power Play (Mixed Doubles only)

Once per game, each team, when they have the decision on the placement of the “positioned” stones, can use the “Power Play” option to position the stones. The Power Play option cannot be used in extra ends.

(a) The in-house stone, which belongs to the team with last stone in that end, is placed with the back edge of the stone abutting the front edge the tee line, with half the stone in the 8-foot and half in the 12-foot circle.

(b) The guard stone is positioned to the side of the sheet, so it would be bisected by a direct line between the middle of the in-house stone to the middle of the hack. The distance of this corner guard from the house will be the same distance that was determined for the center guards.

Sweeping
    
After a stone is thrown, players are allowed to sweep the ice in front of the stone. Sweeping clears the ice of any debris that might slow the stone down or send it off course. Sweeping also melts a thin layer of ice that reduces friction and thus increases the distance the rock travels. 
    
Sweeping is allowed by any player on the throwing team between the two tee-lines. Players are not allowed to sweep opponents stones in that area. 

Behind the tee line at the playing end, only one player from each team may sweep at any one time. This may be any player of the delivering team, but only the skip or vice-skip (third) of the non-delivering team.

Only stones in motion – termed “running stones” – may be swept. Players may not touch any stones while sweeping. Also, they may only sweep in front of the stone, in a direction perpendicular to the direction of motion.

Players are allowed to sweep stones that are set in motion by other stones.

Game Timing

Men's and women's teams have a total of 38 minutes of thinking time for a 10 end game. In addition, each team may call one 60-second timeout during each game to consult with its coach. Each team's clock begins after the opposing team's shot is considered complete and stops once the next stone is delivered. The time must be displayed on a clock clearly visible to the players. If a team’s clock runs out before the completion of the game, the team forfeits the game. Mixed doubles teams receive 22 minutes of thinking. There is a five minute break after the completion of the fourth end in mixed doubles and the fifth end in men's and women's.

If a game requires an extra end or ends, men's and women's teams receive four minutes and 30 seconds of thinking time for each extra end. There will be one-minute breaks between the 10th and 11th end and any subsequent ends. Each team can call one 60-second timeout in each extra end. When extra ends are required in mixed doubles, each team shall receive three minutes of thinking time for each extra end.

Player substitution

If a player is injured and cannot continue to play, or cannot start the game, the team has two choices. One is to continue the game with only three players, with the first and second player in the lineup each throwing three stones. The second is to insert the alternate into the missing players spot at the start of the next end. The playing rotation can be changed when a substitute enters the game. Mixed doubles teams are not permitted a substitute.

Violations

Here is what occurs if the following rules are broken.

Hogline violation: If a player releases a stone after it has touched the hogline, a violation is called and the stone is removed from play. If the stone has hit another stone, all affected stones are put back to their original location.

Touching a moving stone: 1) If a moving stone is touched by anyone on the playing team or their equipment, the touched stone shall be removed from play immediately. The opposing skip may return any stones the touched stone has affect back to their original position. If, however the opposing skip believes the removal of the stone would be beneficial to the offending team, then the skip may place the stone as nearly as possible to the position he or she believes it would have come to rest. That skip may also reposition any stones that would have been displaced had the moving stone not be touched. He also has the choice to leave the stones where they are. 2) If a moving stone is touched by the opposing team, the stone shall be placed where the skip of the team to which it belongs believes to would have come to rest had it not been touched.

Touching a moving stone: Between the tee line at the delivering end and the hog line at the playing end: If a moving stone is touched, or is caused to be touched, by the team to which it belongs, or by their equipment, the touched stone is removed from play immediately by that team. A double touch by the person delivering the stone, prior to the hog line at the delivering end, is not considered a violation. If a moving stone is touched, or is caused to be touched, by an opposition team, or by its equipment, or is affected by an external force: 1) If the stone was the delivered stone, it is redelivered 2) If the stone was not the delivered stone, it is placed where the team to which it belongs reasonably considers it would have come to rest had it not been touched.

Inside the hog line at the playing end: If a moving stone is touched, or is caused to be touched, by the team to which it belongs, or by its equipment, all stones are allowed to come to rest, after which the non-offending team has the option to: 1) remove the touched stone, and replace all stones that were displaced after the infraction to their positions prior to the violation taking place; or 2) leave all stones where they came to rest; or 3) place all stones where it reasonably considers the stones would have come to rest had the moving stone not been touched. If a moving stone is touched, or is caused to be touched, by an opposition team, or by its equipment, all stones are allowed to come to rest, after which the non-offending team places the stones where it reasonably considers the stones would have come to rest, had the moving stone not been touched.

Touching a stationary stone: If a stationary stone which would have had no effect on the outcome of a moving stone is displaced, or caused to be displaced, by a player, it is replaced, by the non-offending team, to their positions prior to the violation taking place. If a stationary stone which would have had no effect on the outcome of a moving stone is displaced, or caused to be displaced, by an external force, it is replaced, with agreement of the teams, to its position prior to the violation taking place. 

If a stone which would have altered the course of a moving stone is displaced, or caused to be displaced, by a player, all stones are allowed to come to rest and then the non-offending team has the option to: (i) leave all stones where they came to rest; or (ii) remove from play the stone whose course would have been altered, and replace any stones that were displaced after the violation to their positions prior to the violation taking place; or (iii) place all stones in the positions the team reasonably considers they would have come to rest had a stone not been displaced. 

If a stone which would have altered the course of a moving stone is displaced, or caused to be displaced, by an external force, all stones are allowed to come to rest, and are then placed in the positions in which they would have come to rest had a stone not been displaced. If the teams cannot agree, the stone is redelivered after all displaced stones have been replaced to their positions prior to the violation taking place. If agreement on those positions cannot be reached, the end is replayed. 

If a displacement is caused by stones deflecting off the sheet dividers, the stones are replaced, by the non-delivering team, to their positions prior to the violation taking place.

Playing out of order: If a player delivers a stone out of proper rotation, the end continues as if the mistake had not occurred. The player who missed a turn delivers the last stone for that team in that end. If it cannot be determined which player delivered out of proper rotation, the player who delivered the first stone in the end for that team delivers the last stone for that team in that end.

Incorrect sweeping: If a stone is swept improperly by a team, the non-offending team has the option of allowing the play to stand, or of placing the stone, and all stones it would have affected, where they would have come to rest had the violation not occurred.

Shooting Percentage

The primary stat used to judge a player’s performance is shooting percentage. This stat is essentially the rate of success the player has during a game. To determine shooting percentage, each shot is evaluated by a scorer on a four-point scale. Four points would be awarded for a perfectly executed shot, three points for a good shot, two points for a poorer shot, and so on. For very difficult shots, bonus points can be awarded, so a player could conceivably score five or six points (out of a possible four) on a particular shot.

A player’s shooting percentage is determined by dividing the number of points awarded by four times the number of shots taken. In a normal, 10-end game, the player’s total points would be divided by 80 (4 points per shot X 2 shots per end X 10 ends) to determine shooting percentage.

Since shots get more difficult as the end goes on, the skip, who shoots last, will generally shoot the lowest percentage and the lead, who shoots first, the highest percentage.

The Participants

Both the men's and women's fields consist of 10 teams. Each team consists of four players and an alternate. The alternate may be substituted prior to any game. He or she is considered part of the team and will receive a medal. The mixed doubles field has eight teams, each consisting of one man and one woman.

Seven nations qualify for the men's and women's tournament based on world championship finishes in the two years prior to the Games (2016, 2017). Points are awarded based on order of finish, with 14 points going to the winner, then 12, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 for second through 12th (points are shared if there were no tie-breakers played). Two more teams emerge from the Olympic Qualification Event in December, while the host, South Korea, has an automatic bid. Mixed Doubles also uses the points accumulated at the previous two world championships to determine it's field.