IN THIS week's Eight Things We Learned, we discover more about Adelaide's scary forward line, Clarko's ruthless selection calls, and more.

Check out what we learned from round four of the 2023 season.

BARRETT Defensive Hardwick facing one of his toughest tests

1) The Dogs have gone to work at centre bounces

The Bulldogs' centre clearance work has been electric in the two weeks since they started the season with back-to-back 50-point losses. The Dogs lost the centre clearance count 15-8 and 12-7 against Melbourne and St Kilda respectively in the opening two rounds, but have completely flipped that script in the past two games, which were both wins against 2022 finalists. The Dogs won the centre clearance count against Brisbane (12-4) and Richmond (16-8), despite losing hit-outs 45-30 against the Tigers. Marcus Bontempelli and Tom Liberatore have both been a huge part of that, along with the under-the-radar Adam Treloar. Sometimes it's simply a territory game and centre clearances offer that with immediacy. - Ben Somerford

2) Adelaide could have the League's best forward line

When Adelaide landed Izak Rankine during last year's Trade Period, there was plenty of talk about how dangerous the Crows' forward line would be in 2023. And after just four games this year, things are starting to click. The Crows have kicked 35 goals in the past fortnight, with Taylor Walker (four), Josh Rachele (three) and Rankine (three) combining for 10 in Saturday's win over Fremantle, while Riley Thilthorpe managed just one after kicking five in the Showdown. Ned McHenry replaced the suspended Luke Pedlar against the Dockers and had 10 score involvements, and the Crows have done it all without the injured Darcy Fogarty and the suspended Shane McAdam in the past two weeks. There is depth, and plenty of excitement. The Gather Round opener against Carlton is going to be must watch. – Dejan Kalinic

3) Aliir is still one of the game's best defenders

Saturday night was a timely reminder that Aliir Aliir is one of the best key defenders in the competition when at his very best. Aliir collected an All-Australian blazer and finished third in the John Cahill Medal at the end of his first season at Alberton, but he didn't reach the same heights in 2022. When Ken Hinkley needed his stars to deliver on the weekend, it was the 28-year-old who produced a dominant display against his old side on his old home ground. Aliir clamped four-time Coleman Medallist Lance Franklin and came up with big plays, including the final one of the game when he swatted Ollie Florent's shot after the siren back into play on the last line of defence. Twelve of Allir's 16 disposals were intercepts – the most on the ground – while Franklin was held goalless and to just one mark. Hinkley made a statement at selection last week by axing one All-Australian defender – Darcy Byrne-Jones – from the 22, but he got a huge response from another. - Josh Gabelich

4) The Cam Rayner experiment down back is over

For the second time in his past five games playing as a forward, Cam Rayner inspired Brisbane to victory with his four goals against Collingwood on Thursday night. In round 22 last year, he did likewise against St Kilda at Marvel Stadium, offering life to a lacklustre performance and getting the Lions over the line in a must-win match. During the pre-season, Brisbane used the former No.1 draft pick in defence, taking him back to a position he excelled in as a junior in the hope his penetrating ball use and aerial prowess could add another element to its backline. Although he played well in the opening three rounds in the back half, Rayner has surely shown once and for all which end of the ground he should be playing at. He can still be a 'break in case of emergency' option in defence, but expect Rayner to be prowling the forward line for most of 2023. – Michael Whiting

5) Cat's importance can't be underestimated

If we needed a reminder of just how important Mitch Duncan is to Chris Scott's side, we got a timely one on Easter Monday. The 31-year-old missed the first three rounds of the season after dealing with a lingering calf issue across February and March, one that sent him to Adelaide to help fast track his return. The numbers jump off the page – 31 disposals, 14 marks and 439 metres gained – but it wasn't about them. While Jeremy Cameron was the star of the show, Tom Stewart dictated traffic down back and everyone had a lick of the ice cream, Duncan provided a calm, guiding head that can't be underestimated. Geelong has struggled without Joel Selwood out there, but it now has Duncan back on the park, and back in business. – Josh Gabelich

6) The Saints' attack is hard to plan for

There's nothing more mysterious in footy right now than St Kilda's forward line, with what would have been an almost predictable attack had Max King and Tim Membrey been available evolving into an unconventional but lethal path to goal. Jack Higgins is the Saints' leading goalkicker, and he's not easy to read at the best of times, while Anthony Caminiti, a 196cm 19-year-old, is now one of the competition's most exciting key forwards despite having not been on an AFL list just eight weeks ago. Then there's Mitch Owens, a midfielder who stood up as the Saints' main target against Gold Coast on Saturday, plus the dash and dare of Dan Butler. Throw in a bevy of midfielders and half-backs that all love to hit the scoreboard and this side becomes very, very difficult to plan for. - Howard Kimber

7) Dees defender is yet another midfield option

Trent Rivers made a "career-defining" move to the backline as a junior footballer that set up his Draft prospects, but he now looks ready to get back into the engine room as a midfield option for Melbourne. The 21-year-old was a regular in the centre against West Coast on Sunday and finished with 27 disposals and three clearances after entering the match with season averages of 20.7 and 0.3. A big pre-season building his endurance and size for a more prominent midfield role looks to be paying off, and the premiership defender looks more than capable of giving the Demons a new look in the centre square whenever needed. – Nathan Schmook

8) North Melbourne is no country for old men

There’s a new world order at North Melbourne, with new coach Alastair Clarkson putting the 'Roo' in 'ruthless' by making bold selection calls on some fan favourites not only before matches, but during them. The Kangaroos raised eyebrows on Good Friday when they subbed contested beast Ben Cunnington out of the game after he failed to make an impact in the first half and replaced him with fellow veteran Hugh Greenwood, who himself had been dropped from the starting 22. It comes after Clarkson dropped veteran ruck Todd Goldstein in round one, instead backing in 24-gamer Tristan Xerri off the back of a strong pre-season. Veterans Jack Ziebell and Liam Shiels as well as Cunnington and Goldstein will continue to play a role this season, but Clarkson has been willing to show that incumbency is no guarantee of selection. – Sophie Welsh

9) The sub rule needs to be tweaked

Round four saw two former skippers named as substitutes via very different approaches. Essendon opted to bring in Andrew Phillips as a late change on Sunday, sparing Dyson Heppell the rigamarole of being 'dropped' during the week - which would have generated headlines - and being re-picked as a substitute. Richmond chose the latter approach, listing Trent Cotchin as a "managed" out on Thursday even though he was always going to play on Saturday, albeit as the sub. The Bombers' tactic could end up being a common one among clubs as they look to manage the workload of veteran players without creating the media storm that Cotchin's absence did this week. This would regularly lead to 'late changes' in the hour before the first siren, unless the procedure is changed to allow the selection of 23 players during the week. – Sarah Black