After round 21 there is little movement in relative rankings, but Sydney and GWS rise into our informally-defined historical “premiership” frame.

However, it’s the increasingly anomalous Port Adelaide, theoretically a contender, which we want to focus on here.

The popular opinion of Port Adelaide being unable to match it with other good sides is well and truly borne out when we dig into their performance on our strength ratings by opponent. We have in the past broken up statistics by top 8 and bottom 10 and used them to call Josh Kennedy (but also Dean Cox) a flat track bully back in 2015. Then in 2016 we ran an opponent-adjusted Coleman to see who was kicking the goals against tough opponents (turns out: Toby Greene and Josh Jenkins). This time we’ve looked at whole teams.

Simply put, Port Adelaide are the best side in the competition against weak opponents and they’re about as good as North Melbourne against the good teams.

Below is a chart where we have calculated strength ratings through the same method as we always do using whole-of-season data, but separate ratings are derived for matches against the top half and bottom half of the competition as determined by our ratings above.

Most clubs, predictably, have done better against the bad sides than the good ones. Port Adelaide, however, take this to extremes. They rate as 120% of league average in their performance against the bottom nine sides. Not even Adelaide or Sydney look that good, over the year, in beating up on the weaker teams.

That’s why we’ve been rating Port so highly this year – their performance, even allowing for the scaling we apply for opponent sets, has been abnormally, bizarrely good to the extent that it’s actually outweighed and masked their weaknesses against quality teams. Their sub-97% rating against top sides is 13th in the league, ahead of only North, Carlton, Fremantle and the Queensland sides. This divergence is more than double the size of the variance for any other team.

It appears that the problem mostly strikes the Power in between the arcs. Against bottom sides, their midfield strength is streets ahead of any other side at 141% of the league average, meaning they get nearly three inside-50s for every two conceded. This opportunity imbalance makes their decent defence look better and papers over a struggling forward line. Against quality sides, that falls apart and they get less inside-50s than their opponents.

Looking elsewhere, Adelaide stands out as looking stronger against quality opposition, with their midfield and offence fairing substantially better than against weaker sides – a couple of whom have, of course, embarrassed them throughout the year

The Hawks and two strugglers in North Melbourne and Carlton also seem to acquit themselves better against the top sides than against their own weight class. For North, their inside-50 opportunities dry up against good sides but they make better use of the forward entries – they rate as above league average, offensively, against the top nine teams. For Carlton, unsurprisingly, it’s their stifling defence who step up, and the same is true of Hawthorn.

St Kilda’s forward efficiency and Richmond’s defensive efficiency have also been a lot higher against top sides, but the converse is true of the two teams’ opposite lines.

At the other end of the table, Geelong, Sydney and especially the Bulldogs are the other finals contenders with the biggest worries about sustaining their output against quality opposition. Sydney’s midfield struggles to control territory, slightly losing the inside-50 battle on average against the top half of the competition while bullying weaker sides (their offensive efficiency is actually slightly higher however). The Bulldogs and Geelong share these midfield issues but their forward lines also struggle under quality defensive heat.

But it really is Port Adelaide who stand out here. Their output against weaker sides is really good and shouldn’t be written off. There’s obviously quality there, and they sit in striking distance of the top 4 with a healthy percentage. However, it wouldn’t be a stretch to call their overall strength rating fraudulent given its composition and we will be regarding them with a bit of an asterisk from here. Unless they can bridge the gap and produce something against their finals peers, even a top 4 berth is likely to end in ashes.