Ice hockey

Each side fields six players at a time: a goaltender and five skaters. Players change on the fly in rolling shifts, so a squad is much larger than the number on the ice and the depth of a roster is a real competitive factor rather than a bench of substitutes.

A game is divided into three periods. The team that scores more goals wins. Goals are worth one each — there is no equivalent of a two- or three-point score — which is why hockey's scoring stays low and a single goal carries weight.

Offside and icing

Two restrictions shape how the puck moves.

• Offside governs entry to the attacking zone: a player may not enter the offensive zone ahead of the puck. The zone is marked by a blue line, which is why attacking play is often about timing a zone entry rather than simply skating forward.
• Icing stops a team clearing the puck from its own half all the way down the ice without it being played. Icing is called and play restarts in the offending team's defensive zone, so it cannot be used as a free escape.

Penalties and the power play

A penalised player leaves the ice for a set period, and their team plays short-handed. A minor penalty lasts two minutes; a major penalty lasts five and does not end early if the opposing team scores. Longer misconduct penalties remove a player without giving the opponent a numerical advantage.

The resulting power play — one extra skater — is the sport's most reliable scoring opportunity, so special teams are a distinct part of a team's quality. A team's penalty kill, played short-handed, is measured separately, and a strong kill can win games on its own.

A team may also pull its goaltender for an extra skater late in a game, accepting a near-certain goal against if it concedes in exchange for a numerical advantage while chasing a result.

Overtime and shootouts

How a tied game is resolved depends entirely on the competition, and this is a frequent source of confusion.

• In many regular seasons, a tie after regulation goes to a short period of overtime, and if it remains level, to a shootout — a one-on-one contest against the goaltender.
• In most post-season hockey, there is no shootout. Overtime is played as sudden death: the first goal wins, and further periods are added until one is scored. A playoff game can therefore run to effectively double or triple its regulation length.

Where the rules differ

How leagues are structured

Ice hockey's leagues do not share one model, and the difference changes what a table means.

• Closed league with playoffs. The largest North American league operates as a closed competition with no promotion or relegation, split into conferences and divisions, where a post-season bracket decides the champion. It has its own hub on this site.
• European leagues with promotion and relegation. Many national leagues in Europe promote and relegate between divisions, and some decide the championship through a post-season series anyway — so a league can have both.
• Points systems differ. Some leagues award two points for any win and one for a loss in overtime or a shootout. Others award three for a regulation win, two for an overtime or shootout win, and one for an overtime or shootout loss. Two identical sets of results can therefore produce different tables in different leagues.
• Continental club competitions bring champions of national leagues together, in a format that has changed between editions.
• International competition is run by the sport's world governing body, with an annual world championship and an Olympic tournament, plus a prominent under-20 championship.

Because a player's statistics are shaped by rink width, the league's points system and the length of a season, comparing scoring across leagues is less reliable than it looks. A transfer that seems obviously strong on paper may not translate.