Rugby, and tournament rugby in particular, is all about trends, with a combination of officiating and coaching innovation producing a unique style every four years.
Typically, the early matches set the tone.
In 2007, we had the tournament of super-slow ball, endless contested kicks and Maginot Line defending. Lax officiating meant it was easy to slow the ball down, get set in numbers and generate massive defensive linespeed. Ireland were badly caught out - though both Leinster and Ireland would use a gameplan based on those ideas to win competitions in 2009.
Four years later, it had swung in a different direction. 2011 was the tournament of the turnover, with the attacking side of the ruck under huge focus and defending poachers given massive leeway. The key tactics of that tournament were the chop tackle and defensive steals.
South Africa’s defeat to Japan has rightly generated all the headlines and provided this year's edition with its breakout moment. The ‘World In Union’ is the official song and it has never felt more appropriate then during that five minutes when every neutral fan was roaring on the Cherry Blossoms.
The sense of drama building throughout the game set social media alight. Casual fans were caught up in the excitement until, by the end, people who barely knew Japan were playing at the tournament were shedding tears at the emotion of it all.
Will the result matter? The sober assessment is that the Boks picked up two bonus points and are still well positioned to qualify and win Pool B. They could easily follow in the footsteps of England in 2007 and France in 2011, both of whom reached the final after poor pool campaigns.
But the positive is bigger than just the result itself. Japan showed that smaller teams, playing rugby with ball in hand, can beat a bigger, more powerful side.
Yes, Japan conceded two tries to rampaging straight charges by Springbok forwards and sheer power will never fully go out of fashion. But Japan’s speed, technique, discipline and accuracy won the day, seeing them dominate the penalty count and leading to that final overlap for Karne Hesketh’s winning try.
The early indications are that it is the defenders who are under the microscope in 2015, with tacklers and poaching techniques being ruthlessly punished by referees. Referees have wised up and even the slightest hint that a tackler is lying in the wrong place to set up a turnover or slow the ball down is leading to the whistle being blown.
The result? This looks like it could be the tournament of quick attacking ball.
That should suit Ireland, as quick ball gives teams who use footwork and passing a chance against those who use favour size, power and the offload (Japan attempted no offloads against South Africa). It also means that, for the first time in a long time, playing through phases is a viable attacking strategy.
And while it was against a weak opponent, Ireland have never looked more like the Leinster team of the Schmidt era than they did on Saturday, using the full width of the pitch, aligning with depth and layers in attack, and passing the ball with real purpose and intent.
One unresolved issue remains whether the Irish lineout will be good enough against the best sides without Devin Toner. Canada simply did not contest at lineout time – coach Kieran Crowley explaining afterwards that he felt the Canadians were simply too small to bother putting jumpers up on Irish ball. So while Ireland posted good stats, the Toner-less lineout has yet to prove itself.
The centre positions are also a key talking point.
Robbie Henshaw can handle a huge range of different situations to the point that the number on his back is irrelevant. His size, timing and tackling power make him a key defender while his footwork and explosiveness are vital assets to Ireland's attack.
But the question of who should partner him remains a live one.
Luke Fitzgerald is an excellent defender and, like Henshaw, is comfortable in a wide range of situations across the backline. He did his chances no harm against Canada, earning praise from Schmidt for his distribution.
Darren Cave is likely to get a chance next week and is a classic attacking number 13 while Payne, who moves between 13 and 15 and is also at his best in the wide channels, is the incumbent in the position. One to watch.
Scrum-half is also a position worth watching. In his quiet way, Eoin Reddan had a game-changing impact on Saturday, dramatically lifting Ireland’s tempo in the last 15 minutes.
Ireland hadn’t scored in 25 minutes of second-half action before the 34-year-old came on. By the final whistle, a further 21 points had been added in just 15. Reddan's greatest asset is his natural urgency and he is at his best when working with quick, clean ball. That could yet see him become more and more important to Ireland’s cause as this tournament develops.
