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The New Zealand All Blacks practice lineouts at Trusts Stadium in Auckland, New Zealand. ((Phil Walter/Getty Images))

The Rugby World Cup kicks off Friday in New Zealand with Canada and 19 other countries looking to make their mark at the sport's biggest showcase. Here is a list of things to look for:

1. Respect The Ref

Rugby is a complicated sport with plenty of room for rule interpretation. But game referees do their best to let teams know what's what as play goes on, offering a steady stream of advice and warnings that is captured by microphones for television purposes. It can make for a fascinating play-by-play within the game.

2. Beware The Breakdown

Rugby is all about ball possession with ball-carriers having to release it when tackled. The tackler, meanwhile, has to release the ball-carrier so he can place the ball. But if the tackler keeps his feet, he can then try to play scavenger while the ball-carrier's teammates look to protect the ball and clear out the opposition. New Zealand's Richie McCaw, Australia's David Pocock and South Africa's Heinrich Brussow are masters at stealing the ball at the breakdown. How referees call the battle at the breakdown is often key to the game.

3. Marvelous Big Men

Tonga prop Soane Tonga'uiha (6-foot-3, 286 pounds) is just one of the man-mountains who will serve as ball-carrying battering rams. South African prop Tendai Mtawarira is smaller (six foot, 246 pounds) but fans will chant his nickname — Beast — whenever he runs with the ball. Scottish lock Richie Gray stands 6-foot-9 and can run. Six-foot-seven English lock Courtney Lawes is another athletic specimen who moves well and can destroy with a tackle. Watch for South Africa lock Bakkies Botha, one of rugby's hard men.

4. One Tough Sport

When rugby players go down on the field, play often continues. Trainers rush on and attend to the injured while the battle rages elsewhere, although the referee will stop the game if the action gets too close to the injured player.

5. TV Match Official 

Unlike some sports, rugby has television replay down pat. When it comes to scoring plays, the referee can go to the television match official for guidance. It usually doesn't take long either.

6. The Offload Pass

A prominent feature of rugby league that has come to rugby union, the offload is the art of passing the ball while being tackled. Done correctly it continues the attack and, if defenders slow down thinking the tackle was made, can create openings. Rugby league convert Sonny Bill Williams of New Zealand is a master of the offload.

7. Expect Empty Benches

World Cup teams will dress seven substitutes and will usually throw all of them on before the game is over. The constant stream of bodies coming in from the sidelines is a bone of contention for some fans. Props are often the first to come off. Coaches also look for some substitutes to function as impact players, making a splash off the bench.

8. Watch The Kickers

Winning rugby teams keep the scoreboard turning over, usually thanks to the kickers who look to punish the opposition when penalties are given in striking range of the posts. New Zealand's Dan Carter, England's Jonny Wilkinson and South Africa's Morne Steyn are kicking machines. Some teams also have a long-range kicking specialist.

9. We Are The World

National rugby teams these days are a melting pot, thanks to residency rules. New Zealanders James Arlidge, Justin Ives, Luke Thompson, Murray Williams and Shaun Webb, Tongans Ryukoliniasi Holani and Sione Talikavili Vatuvei, Australian Ryan Nicholas and Samoan Alisi Tupuailai are on Japan's roster. England's lineup features eight players born elsewhere including Manu Tuilagi whose brother Alesana Tuilagi is with the Samoan team.

Australian star Quade Cooper was born in New Zealand while New Zealand's Ben Franks was born in Australia.

Pacific Islanders pop up on all sorts of teams. Wales' Toby Faletau hails from Tonga, for example, as does American Matekitonga Moeakiola.

Canada's imports include James Pritchard (Australia), DTH van der Merwe (South Africa), Ander Monro (Scotland), Nanyak Dala (Nigeria) and Jeremy Kyne (New Zealand). Monro, Dala and Kyne make their home in Victoria, Saskatoon, and Edmonton, respectively. Monro was born in Canada to Scottish parents and raised in Scotland.

And Canadian Robert Barbieri plays for Italy.

10. Lament Those Missing

While some stars are absent through injury, there are players not at the World Cup because of where they play their rugby. Former All Black Nick Evans would be a perfect backup to fly half Dan Carter but for the fact that he plays in England for Harlequins. Same for high-stepping South African hooker Schalk Brits, who plays for Saracens in England.