THIS season has marked the first time in 22 years North Melbourne has topped the competition for fewest points conceded.

According to AFL statistician Cameron Sinclair, we have to go back to the end of round two, 1996, for the last time North previously boasted the lowest points against figure.

The Kangaroos held that top ranking for just one round, and in that premiership year would finish the home and away season ranked seventh.

That was one of the better defensive results achieved in coach Denis Pagan's glorious 1993-2002 reign, when the Kangaroos relied on an awesome attacking arsenal led by Wayne Carey to blast opponents off the park.

In their other premiership year under Pagan, 1999, the Roos were ranked 10th in points conceded.

The Kangaroos class of 2018, however, has a stingier defensive edge.

It has held the top defensive ranking at the end of five of this year's 10 completed rounds, including the past two.

Remarkably, until this season, North, under coach Brad Scott, had been a team that – like Pagan's powerhouse sides – relied on attack rather than defence.

From 2010-17, Scott's team ranked better than eighth for points conceded just once (fifth in 2014) and 12th or worse in four of those eight seasons, including 2015 when they reached their second consecutive preliminary final.

What's changed at Arden St since the end of last season – when only Gold Coast and the Brisbane Lions conceded more points – to make North such a formidable defensive outfit?

It hasn't followed Richmond's lead and based its defence around locking the ball inside its forward half, having only marginally improved in this area.

However, the Kangaroos are defending much better once the ball enters their defensive half.

According to a former opposition analyst, North has improved its ability to both slow down their opponents' ball movement and to maintain a strong defensive structure behind the ball.

"Their defenders hold their shape, which forces teams to go wide with their inside 50 entries and, in turn, allows North to better absorb those entries," he said.

Scott last week described North's defensive improvement as an evolution rather than a revolution, but Champion Data statistics suggest otherwise.

Let's start with the Roos' ability to put pressure on opposition disposals.

Last year, they were ranked 14th in pressure factor – the physical and implied pressure a team puts on opposition ball-handlers (including tackles, corralling, closing space and chasing) – but they have climbed to second this year.

Their ability to shut down goals from the corridor has also gone through the roof (17th in 2017 to second).

The added defensive run Ben Jacobs, Jed Anderson and Jy Simpkin have given North's midfield this year has been a factor, while small forward Kayne Turner is lauded at Arden St for the defensive pressure he applies inside the Roos' forward 50.

Once the ball enters North's defensive 50, its backline, led by veterans Robbie Tarrant and Scott Thompson, ups the ante.

The Kangaroos are ranked first in the AFL for scores conceded from opposition inside 50s and points conceded from intercepts. They are also second in defensive efficiency, having conceded a stunning 34.5 points fewer than last year for every 50 minutes the ball is inside their back half.

In each of these three categories, North was ranked 15th or worse in 2017.

Evolution or revolution? We'll let you be the judge.

North's defensive Roo-volution

Opposition scoring sources

Statistics courtesy of Champion Data