A full 17-match Round Robin. A guaranteed return Derby match in Round 18. Then four matches to complete the schedule, carefully chosen to achieve a proper handicap. What’s not to like?
What Does 17-D-4 Do Better than the Alternatives?
|Return matches based on last year’s ladder||Return matches based on this year’s ladder (actual strength)|
|Clubs grouped by six, #7 gets much easier draw than #6||Toughness of draw scales with the strength of the team, no arbitrary blocks|
|Everyone gets a bye the week before the finals to discourage resting of star players||Everyone gets a bye in the last five weeks before finals; the best teams get it later|
|Prime timeslots late in the season contain mismatches||Schedule them when you know who is actually good|
|Top six after 17 weeks guaranteed a home final||Every position open until the last match|
|Local rivalries not played twice||All rivalries played in the special Derby Round|
|The last five rounds have to be fixtured in a hurry||There is an extra week during Derby Round, so you can take a couple of days to get it right|
|Home-Away balance not achievable unless all blocks have exactly three teams who have played 9 Home / 8 Away||Every team gets 9 Home / 9 Away in the first 18, then 2 Home / 2 Away selected from unplayed return legs|
And What Won’t it Solve?
- For that, use a more targeted points-based draft system
- Some matches being more important than others
- Any finals system is vulnerable to this. In the AFL, there are sharp divisions between 8 & 9, and between 4 & 5 that have huge rewards.
- Some teams being crap
- Mismatches will happen. There will be fewer under 17-D-4 because teams play their return matches against teams of similar strength
Let’s pretend that each team has played a single round-robin. In Round 18 (or Round 19 with the current counting for the early bye), each team plays its local rival. If they don’t have one, we’ll make them up for now. Clubs would have some say in this.
We assume that a good estimate of a team’s strength is the number of games it has won out of those 17. Looking at 2016’s ladder after 17 matches:
That Target is the combined number of points that we want the team’s last five opponents to sum to — including their Derby rival. The average team has scored 34 points, so the average five-week schedule comes to 170 points. I’ve used a scaling factor of 1.5 to give stronger teams stronger opponents, but that number is malleable. Note: a perfectly fair draw would give the bottom teams a higher Target than the top teams, to account for self-reference. That would be a scaling factor of -1.0.
I’ve written a tree search program that finds close fits to the target totals, choosing matches from the return legs that have not yet been played. In the fixture below, every team is within 13 points of the target opponent strength (or an average of 2.6 per opponent, less than one win). For instance, Hawthorn’s opponents would be Geelong (already fixtured, 48) + West Coast (48) + Sydney (48) + Carlton (24) + St Kilda (36) for a total of 204, compared with a target of 203.
|Haw||203||204||Geel||WCE, Syd, Carl, St.K|
|GWS||191||192||Syd||Ess, N.M., W.B., WCE|
|Syd||191||204||GWS||Geel, G.C., Melb, Haw|
|Geel||191||192||Haw||B.L., P.A., Syd, Adel|
|WCE||191||192||Freo||W.B., GWS, Rich, Haw|
|Adel||191||180||P.A.||Geel, Rich, Coll, N.M.|
|W.B.||191||188||St.K||P.A., GWS, G.C., WCE|
|N.M.||185||188||Melb||Adel, Coll, St.K, GWS|
|St.K||173||164||W.B.||Haw, N.M., Freo, Ess|
|P.A.||167||164||Adel||B.L., Freo, Geel, W.B.|
|Melb||161||168||N.M.||Carl, Syd, G.C., Rich|
|Coll||161||156||Carl||Adel, Rich, Freo, N.M.|
|Rich||161||156||Ess||Melb, WCE, Coll, Adel|
|Carl||155||144||Coll||Haw, G.C., B.L., Melb|
|G.C.||155||156||B.L.||Melb, W.B., Carl, Syd|
|Freo||137||148||WCE||Coll, St.K, P.A., Ess|
|B.L.||131||132||G.C.||Carl, Ess, P.A., Geel|
|Ess||125||132||Rich||Freo, St.K, GWS, B.L.|
We can then shuffle these 36 matches across five weeks, giving the top four a bye in the last round, and the next four a bye in the second-last round.
- Syd v Geel, WCE v GWS, G.C. v W.B., Carl v Haw, N.M. v Adel, P.A. v B.L., Freo v St.K, Rich v Melb (Ess, Coll byes)
- GWS v N.M., WCE v W.B., Haw v Syd, Geel v P.A., Adel v Rich, Ess v St.K, Freo v Coll (B.L., G.C., Carl, Melb byes)
- W.B. v GWS, Haw v WCE, Syd v G.C., B.L. v Ess, Adel v Geel, N.M. v Coll, Melb v Carl (Freo, P.A., St.K, Rich byes)
- St.K v Haw, Coll v Rich, GWS v Ess, Melb v Syd, Carl v G.C., P.A. v Freo, Geel v B.L. (Adel, WCE, W.B., N.M. byes)
- Rich v WCE, W.B. v P.A., Coll v Adel, St.K v N.M., G.C. v Melb, B.L. v Carl, Ess v Freo (Haw, GWS, Geel, Syd byes)
I noticed after I’d done this that I’d forgotten to enforce the constraint of Fremantle and West Coast not both playing at home in the same week, so I’ll leave that as an exercise for the reader.
Feedback welcome here and on Twitter.
2 thoughts on “The 17-D-4 AFL Fixture”
Your analysis of 2016 ignores the fact that some teams have not played others at all and have played some twice by round 17. More crucially the principal you outline still does not give an even draw as a top team having a number of opponents just outside the 8 and another top team at home will have an advantage. It would be far better than the current system though.
Hi Brett, thanks for the comment. At the start of the 2016 Example section I did say “Let’s pretend that each team has played a single round-robin.” Yes, the number of wins from Rounds 1-18 2016 contains some bias, I’ve just used it as a starting point for the example in the absence of a true Round Robin. I’ve also got a 2015 example using a proper round-robin chosen from the full season, but didn’t want to wait until Round 23 this year.\n\nI think the advantage you’re talking about by hosting a top team is virtually zero, balanced by away games against middling opponents who become more dangerous at home. Home Ground Advantage measured between home & away performance is not correlated with ladder position from what I’ve seen.