The Suns' victory over the Saints in the first round of the 2013 season was heralded as an "upset win" for the Suns and one of the greatest in their short history. Undoubtedly their win was unexpected, but even the bookmakers rated the Suns as only $3.75 chances, so it was hardly a Halley's comet-like occurrence.

Had I bookmaker data for every game in the 116-year history of the VFL/AFL - indeed, if even such a data source existed - I could use it to determine which victories were relatively unexpected, which were very much expected, and which were considered almost impossible before they transpired. But, I don't have that data.

What I do have, having just created it, is the timeseries of every team's MARS Rating prior to every game ever played. One measure I could use then of the relative likelihood of a game's result is the difference between the MARS Rating of the victor and the loser. If that difference is large and negative for a particular game then I have some grounds for declaring the result of that game an "upset".

With this MARS Differential as the metric, here then are the five greatest upsets in VFL/AFL history, presented in faux suspense-building reverse order:

#5: St Kilda v Geelong 1980 (Round 19)

Ratings Differential: -82.0 (947.0 - 1,029.0)

Result: St Kilda 88 - Geelong 83

St Kilda came into this match second-last on the ladder with a 4-1-14 record and a 69 percentage, facing the second-placed Cats with a 14-0-5 record and a 124 percentage.

The Saints' most-recent three outings had not gone well. In Round 16 they'd lost to first-placed Richmond 222-70; in Round 17 fifth-placed Collingwood had towelled them up 211-107; and in Round 18 they'd gone down to Footscray, who were just one place above the Saints on the ladder, 104-80. In aggregate, across those three games they'd conceded 537 points while scoring just 257 themselves. 

By half-time in their game against the Cats they trailed 4.5 to 5.10, but they rallied in the third term and hung on in the final term to eventually win by 5 points. I think "upset" is a reasonable designation of this result.

#4: Sydney v Melbourne 1993 (Round 13)

Ratings Differential: -86.0 (916.6 - 1,002.6)

Result: Sydney 149 - Melbourne 109

Prior to this game Sydney had lost all 11 games in the current season having finished the previous season with just 3 wins and a draw from 22 games. Melbourne weren't having a fantastic year in 1993 but were 5 and 6, lying 10th on the ladder, and had a 108 percentage.

The Swans' last three games had all been losses - to Richmond, who were second-last on the ladder, by 29 points; to West Coast, who were third, by 57 points; and to Footscray, who were tenth, by 25 points. Melbourne, in contrast, came into the game with considerable form, having knocked off third-placed Essendon by 34 points and fourth-placed Collingwood by 51 points in their last two outings.

The teams were locked at 34-all at the end of the first term, before Sydney eked out a tiny 70-67 lead by the main break. In the third term the Swans kicked 10.4 to Melbourne's solo behind, which gave the Swans a lead too big for Melbourne to run down in the final term.

#3: Sydney v West Coast 1992 (Round 2)

Ratings Differential: -86.4 (958.5 - 1,044.8)

Result: Sydney 98 - West Coast 95

Neither team had any current-season form going into this clash, with both having received byes in the first round of that year, but they'd finished the previous season with MARS Ratings even further apart, MARS' carryover adjustment serving to move both of their Ratings closer to 1,000 at the start of the new season.

West Coast were coming off a 19 and 3 home and away record from 1991 and were losing Grand Finalists, while the Swans had finished 12th with just 7-and-a-half wins in 22 games and a disappointing back end to the season. In the last five games of 1991 Sydney had gone 1 and 4, registering their sole win against the last-placed Fitzroy while recording losses to St Kilda, Geelong, North Melbourne and the Dons - which, in a perverse quirk of the draw, were all teams in the top 5 at the time and therefore vying for Finals berths.

At half-time the Swans trailed by 59 to 48, and by three-quarter time they'd done only enough to lead by 2 points. A low-scoring final term saw the Swans kick 3.4 to the Eagles' 3.3, which was enough - just - to get the Swans home by 3 points.

#2: Brisbane v Hawthorn 1989 (Round 20)

Ratings Differential: -93.3 (965.0 - 1,058.3)

Result: Brisbane 77 - Hawthorn 61

Hawthorn were atop the ladder going into this match with a 17 and 2 record and a 151 percentage, pitted against a Brisbane who were in last place with a 5 and 14 record and a 74 percentage. Brisbane had lost two of their last three games, including one to ninth-placed Sydney by 25 points, while the Hawks were on the tail end of an 8-game winning streak.

Brisbane trailed by 2 points, 12-10, after a very low-scoring first term, but kicked 4.1 to the Hawks' 1.1 in the second term to go into the main break leading by 16 - as it turned out, the margin by which they would eventually win despite being outscored 3.2 to 4.3 by the Hawks in the final term.

Despite the loss to Brisbane, Hawthorn would go on to win the Grand Final of that year 144-138 against the Cats. Brisbane, buoyed by their win against the Hawks, would win their last two games of the season to finish 10th with an 8 and 14 record.

#1: Fitzroy v West Coast 1991 (Round 24)

Ratings Differential: -109.3 (945.4 - 1,054.7)

Result: Fitzroy 99 - West Coast 89

This is another example of an upset where the ladder-leaders are toppled by the cellar-dwellers.

At the end of Round 23 in 1991 West Coast were first with a 19 and 2 record and a 167 percentage, and Fitzroy were last with a 3 and 18 record and a 65 percentage. In the previous week Fitzroy had lost by 46 points to 12th-placed Sydney, erasing any joy they'd felt from toppling North Melbourne, who were Finals aspirants, by a single point in the previous round. That win had followed a 126-point drubbing of Fitzroy by the second-placed Hawks in Round 21. These results hadn't helped Fitzroy's already low Rating which was just 972.6 coming into the season, the result of a lucklustre 1990 in which they finished third-last with a 7 and 15 record.

West Coast, in comparison, had entered the season Rated 1,006.0 on the back of a solid if not exceptional 1990 from which they emerged as losing Preliminary Finalists.

The game started off much as would be expected leaving a wayward Fitzroy trailing an only slightly less-wayward West Coast 1.9 to 5.11 at the main break. Fitzroy then unleashed a 6.5 to 0.3 third-quarter performance to lead by 12 points at the final change, which proved to be enough despite a 7.3 final term from the Eagles.

Whether or not you agree that these 5 contests were the greatest upsets of all time, it's hard to argue that they weren't at least very surprising results. In the table that follows I've included some more surprising results, all of them involving a MARS Differential of at least 50 Rating Points.

(Please click the image for a larger version.) 

ANTI-UPSETS

This blog has so far focussed on the upset result, where a team with a much lower MARS Rating has toppled a team with a much higher Rating.

There have been other games though - lots of them - where the MARS Differential has been as chasmic or even moreso, but where the higher-Rated team has prevailed. The following list shows the result of every game where the MARS Differential between the winning and losing team has been 80 Ratings Points or more.

 There are at least a couple of games in that list worthy, I think, of mention: 

• The Carlton v Sydney game, third on the list, where the Swans almost pulled off what would have been, according to the MARS Differential metric, the second-greatest upset of all time. In that game, the Swans trailed at every change but finished 4.6 to the Blues 1.5 to wind up just a point short of a draw. The Swans went into the game, the last of the home-and-away season, 1 and 18 to the Blues' 12 and 7
• The Geelong v St Kilda game of 1899, which finished up as a 162-1 victory by the Cats. I've double-checked and that score is correct. It was the second-last game of the season that year, there being only Divisional Finals to determine the two Grand Finalists to play in the next week. Neither Geelong nor the Saints were capable of making the Granny before the game started, and the Saints apparently lost interest having racked up their lone point in the first term. The result could have been even worse for St Kilda had Geelong kicked straight that day: the Cats' final score was 23.24. 

(If you want to check out the scoring details of any of the games in this blog, head over to the stats.rleague.com site.)