Ice hockey is a team sport played on ice, in which skaters use sticks to direct a puck into the opposing team's goal. It is a fast-paced physical sport. Ice hockey is most popular in areas that are sufficiently cold for natural reliable seasonal ice cover, such as Canada, the Czech Republic, Latvia, the Nordic countries (especially Finland and Sweden), United States, Russia, Slovakia, Germany, Austria and Switzerland. With the advent of indoor artificial ice rinks it has become a year-round pastime in these areas. In the United States, ice hockey is the lesser of the four major professional sports, but is followed almost religiously in Canada. In North America, the National Hockey League (NHL) is the highest level for men and both the Canadian Women's Hockey League (CWHL) and the Western Women's Hockey League (WWHL) are the highest levels for women. It is the official national winter sport of Canada, where the game enjoys immense popularity. While there are 68 total members of the International Ice Hockey Federation (IIHF), 162 of 177 medals at the IIHF World Championships have been taken by seven nations: Canada, the Czech Republic, Finland, Russia, Slovakia, Sweden and the United States. Of the 64 medals awarded in men's competition at the Olympic level from 1920 on, only six did not go to the one of those countries. All 12 Olympic and 36 IIHF World Women Championships medals have gone to one of those seven countries, and every gold medal in both competitions has been won by either Canada or the United States.
While the general characteristics of the game are the same wherever it is played, the exact rules depend on the particular code of play being used. The two most important codes are those of the International Ice Hockey Federation (IIHF) and of the Canadian founded and North American expanded National Hockey League (NHL). Ice hockey is played on a hockey rink. During normal play, there are six players, including one goaltender, per side on the ice at any time, each of whom is on ice skates. The objective of the game is to score goals by shooting a hard vulcanized rubber disc, the puck, into the opponent's goal net, which is placed at the opposite end of the rink. The players may control the puck using a long stick with a blade that is commonly curved at one end. Players may also redirect the puck with any part of their bodies, subject to certain restrictions. Players may not hold the puck in their hand and are prohibited from using their hands to pass the puck to their teammates, unless they are in the defensive zone. Players are also prohibited from kicking the puck into the opponent's goal, though unintentional redirections off the skate are permitted. Players may not intentionally bat the puck into the net with their hands. Hockey is an "offside" game, meaning that forward passes are allowed, unlike in rugby. Before the 1930s hockey was an onside game, meaning that only backward passes were allowed. Those rules favored individual stick-handling as a key means of driving the puck forward. With the arrival of offside rules, the forward pass transformed hockey into a truly team sport, where individual performance diminished in importance relative to team play, which could now be coordinated over the entire surface of the ice as opposed to merely rearward players. The five players other than the goaltender are typically divided into three forwards and two defensemen. The forward positions consist of a centre and two wingers: a left wing and a right wing. Forwards often play together as units or lines, with the same three forwards always playing together. The defencemen usually stay together as a pair generally divided between left and right. Left and right side wingers or defencemen are generally positioned as such based on the side on which they carry their stick. A substitution of an entire unit at once is called a line change. Teams typically employ alternate sets of forward lines and defensive pairings when shorthanded or on a power play. Substitutions are permitted at any time during the course of the game, although during a stoppage of play the home team is permitted the final change. When players are substituted during play, it is called changing on the fly. A new NHL rule added in the 2005-2006 season prevents a team from changing their line after they ice the puck. The boards surrounding the ice help keep the puck in play and they can also be used as tools to play the puck. Players are permitted to "bodycheck" opponents into the boards as a means of stopping progress. The referees, linesmen and the outsides of the goal are "in play" and do not cause a stoppage of the game when the puck or players are influenced (by either bouncing or colliding) into them. Play can be stopped if the goal is knocked out of position. Play often proceeds for minutes without interruption. When play is stopped, it is restarted with a faceoff. Two players "face" each other and an official drops the puck to the ice, where the two players attempt to gain control of the puck. Markings on the ice indicate the locations for the "faceoff" and guide the positioning of players. There are three major rules of play in ice hockey that limit the movement of the puck: offside, icing, and the puck going out of play. The puck goes "out of play" whenever it goes past the perimeter of the ice rink (onto the player benches, over the "glass", or onto the protective netting above the glass) and a stoppage of play is called by the officials using whistles. It also does not matter if the puck comes back onto the ice surface from those areas as the puck is considered dead once it leaves the perimeter of the rink. Under IIHF rules, each team may carry a maximum of 20 players and two goaltenders on their roster. NHL rules restrict the total number of players per game to 18 (traditionally twelve forwards and six defencemen) plus two goaltenders.
Since ice hockey is a full contact sport and body checks are allowed, injuries can be a common occurrence. Protective equipment is highly recommended and is enforced in all competitive situations. This usually includes a helmet, shoulder pads, elbow pads, mouth guard, protective gloves, heavily padded shorts (also known as hockey pants), athletic cup, shin pads, skates, and (optionally) a neck protector. In addition, goaltenders use different gear, (optionally) a neck guard, chest/arm protector, blocker, catch glove, and leg pads. A professional game consists of three periods of twenty minutes each, the clock running only when the puck is in play. The teams change ends for the second period, again for the third period, and again at the start of each overtime played. Recreational leagues and children's leagues often play shorter games, generally with three shorter periods of play. Various procedures are used if a game is tied. In tournament play, as well as in the NHL playoffs, North Americans favor sudden death overtime, in which the teams continue to play twenty minute periods until a goal is scored. Up until the 1999-2000 season regular season NHL games were settled with a single five minute sudden death period with four players (plus a goalie) per side, with both teams awarded one point in the standings. From 1999-2000 until 2003-04 the National Hockey League decided ties by playing a single five minute sudden death overtime period with each team having four players (plus a goalie) per side to "open-up" the game. In the event of a tie, each team would still receive one point in the standings but in the event of a victory the winning team would be awarded two points in the standings and the losing team one point. The only exception to this rule is if a team opts to pull their goalie in exchange for an extra skater during overtime and is subsequently scored upon (an 'Empty Net' goal), in which case the losing team receives no points for the overtime loss. International play and several North American professional leagues, including the NHL (in the regular season), now use an overtime period followed by a penalty shootout. If the score remains tied after an extra overtime period, the subsequent shootout consists of three players from each team taking penalty shots. After these six total shots, the team with the most goals is awarded the victory. If the score is still tied, the shootout then proceeds to a sudden death format. Regardless of the number of goals scored during the shootout by either team, the final score recorded will award the winning team one more goal than the score at the end of regulation time. In the NHL if a game is decided by a shootout the winning team is awarded two points in the standings and the losing team is awarded one point. Ties no longer occur in the NHL.