Month: March 2014

The Strange Case of Melbourne vs West Coast

The West Coast Eagles flexed their wing-muscles again this weekend, beating up a bottom-four team for the second week in a row as Melbourne got well and truly towelled up by the visitors. What was surprising was to see that Melbourne had more disposals, contested possessions and tackles than the Eagles, yet still managed to lose by 93 points. Commentators are always quick to say that a key to winning is to “win the contested ball” and “maintain possession”. But if you were to look at just the stats (excluding the score), you would be excused for thinking the contest was much closer than the score line says.

Historically, number of disposals correlates reasonably well with final margin (with some scatter). Unsurprisingly, teams that possess the ball more typically outscore their opponents.

disp_diff_vs_margin

Melbourne (red) do not seem to deserve to have lost this game by so much!

Melbourne had more disposals than West Coast. So it seems like this game was an outlier. Did Melbourne get a lot of soft possessions in their back line? Well Melbourne only had 14 fewer inside fifties. As you might expect, inside 50s are also a very good indicator of margin.

i50_diff_vs_margin

This game still seems to have been an extreme outlier

 

But you can see that this still does not explain why Melbourne was beaten by so much! Having a few less inside fifties per quarter puts you at a disadvantage, but can’t explain a 93 point margin! The result makes more sense if we look at how a team’s score depends on forward-line efficiency. We would expect that, everything else being roughly equal, a team’s score is a linear function with scoring efficiency. And that is what we see:

goalsperi50_vs_score

Melbourne (red) were extremely inefficient in their forward 50 on the weekend.

The upper bound to a team’s score is dictated by their forward-line efficiency (which is fairly linear in the above plot). That is to say, at a fixed inside-50-to-goal conversion rate, there is a maximum score you can get because there are only so many times you can get the ball up there in a match. And the better this conversion rate is, the higher the score. The area underneath this limit is filled in by teams that function at reasonable efficiency, but just can’t get the ball into their forward line enough (i.e. are outplayed elsewhere on the ground). But Melbourne didn’t fall into that category on the weekend. The red point (Melbourne) is not sitting in the average-goals-per-inside-50-but-low-score region (where forward lines function okay, but just don’t get it enough), they are in the terribly-low-goals-per-inside-50-and-low-score  region! Melbourne didn’t get smashed because their forward line was starved, they lost because their forwards couldn’t turn an inside 50 into a goal.

The numbers show that Melbourne’s game doesn’t fall into a category where West Coast were simply far too good and beat Melbourne all across the ground – Melbourne matched it with the Eagles in many areas, including disposals, tackles and clearances, and weren’t smashed in inside 50s. But still lost by 93 points. The reason that Melbourne didn’t walk away with a more-respectable 5/6 goal loss is that they had a shocking conversion rate in their forward line. I suppose the silver lining is that this probably bodes well for Melbourne once they can get Mitch Clarke, Chris Dawes and Jesse Hogan back in the forward line.

 

 

 

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Round 2 Predictions

All right, first round down! And there’s no complaining about some of the results. We are off to a flying start with 92% return on investment for round 1 for head to head bets, and 125% return on capital. Line bets broke about even (2% return on investment) – unfortunately Brisbane fell apart against Hawthorn in the last quarter and were pipped at the line by half a point! Not to worry – here are the tips and bets for this round!

Tips, chances and margins (predicted winners – NOT bets – in bold)
Richmond ($1.7) (60%) vs Carlton ($2.3) (40%)
Predicted margin: 10.3. Home ground advantage: 5.1

Essendon ($3.0) (38%) vs Hawthorn ($1.4) (62%)
Predicted margin: -10.6. Home ground advantage: 6.9

St Kilda ($1.9) (79%) vs Greater Western Sydney ($2.0) (21%)
Predicted margin: 30.2. Home ground advantage: 11.8

Port Adelaide ($1.7) (54%) vs Adelaide ($2.3) (46%)
Predicted margin: 4.6. Home ground advantage: 3.0

Fremantle ($1.1) (85%) vs Gold Coast ($9.2) (15%)
Predicted margin: 39.1. Home ground advantage: 13.7 (2.9, 6.8, 4.0)

Sydney ($1.5) (59%) vs Collingwood ($2.9) (41%)
Predicted margin: 9.4. Home ground advantage: 6.4

Brisbane ($4.0) (39%) vs Geelong ($1.3) (61%)
Predicted margin: -9.0. Home ground advantage: 11.1

Melbourne ($7.0) (38%) vs West Coast ($1.1) (62%)
Predicted margin: -10.9. Home ground advantage: 13.4

Bulldogs ($3.4) (33%) vs Kangaroos ($1.4) (67%)
Predicted margin: -15.5. Home ground advantage: 3.0

 

Head-to-Head Bets
Bet 7.0% of pot on Essendon at 3.010
Bet 56.0% of pot on St Kilda at 1.917
Bet 19.0% of pot on Brisbane at 3.970
Bet 27.0% of pot on Melbourne at 7.040
Bet 5.0% of pot on Bulldogs at 3.350

 

Line Bets
Line bet 6.0% of pot on Richmond at 1.952
Line bet 10.0% of pot on Essendon at $2.02
Line bet 30.0% of pot on Brisbane at $1.917
Line bet 56.0% of pot on Melbourne at $1.952

Round 1 – Part 2

After a brilliant start to the year (doubling our money already!) thanks to a GWS upset (that we suggested a bet on), our algorithm disagrees with the bookies again for much of the remainder of the round. Maybe they’re placing too much emphasis on pre-season form or new coaches (ahem, Paul Roos). Or perhaps injuries or some other factors that we don’t take into account are affecting the odds. The discrepancies lead to large bets on St. Kilda, who should be favourites against Melbourne, and the Kangaroos, who should be stronger favourites against Essendon. Again, we use odds from here (from 3 days prior to the first game of the week).

Tips, chances and margins (predicted winners – NOT bets – in bold)
Geelong (68%) to win by 18 points against Adelaide (32%).
Kangaroos (69%) to win by 19 points against Essendon (31%).
Hawthorn (77%) to win by 28 points against Brisbane (23%).
St. Kilda (78%) to win by 29 points against Melbourne (22%).
West Coast (65%) to win by 15 points against Bulldogs (35%).

Head-to-head Bets
Bet 22.5% of pot on the Kangaroos at $1.667
Bet 63.3% of pot on St. Kilda at $2.47

Line Bets
Bet 21.5% of pot on the Kangaroos to win by more than 7.5 points
Bet 34.4% of pot on Brisbane to win/lose by less than 46.5 points
Bet 69.5% of pot on St. Kilda to win/lose by less than 10.5 points
Bet 10.7% of pot on the Bulldogs to win/lose by less than 22.5 points

Kicking off 2014 bets – Round 1

Welcome to the 2014 AFL premiership season of betting at AFLpredictions! While I’m still ironing a few things out in the latest iteration of the algorithm, here are the predictions for the first half of the first round. Odds are taken from here. The last few years we have had some good wins in the first round, so we’re looking for good showings from Collingwood and Greater Western Sydney this week!

Tips, chances and margins (predicted winners – NOT bets – in bold)
Collingwood (52%) to win by 2 points against Fremantle (47%).
Greater Western Sydney (16%) to lose by 37 points against Sydney (83%).
Gold Coast (40%) to lose by 8 points against Richmond (59%).
Carlton (60%) to win by 11 points against Port Adelaide (39%).

Head-to-head Bets
Bet 12.6% of pot on the Collingwood at $2.21
Bet 8.9% of pot on Greater Western Sydney at $12.50

Line Bets
Bet 24.0% of pot on Greater Western Sydney to win/lose by less than 48.5 at $1.952
Bet 13.6% of pot on Collingwood to win/lose by less than 5.5 at $1.952

 

 

We’re Back in 2014!

With the first round only a week away, stand by for AFLpredictions (hopefully) triumphant return. The algorithm has been tweaked and improved, so we’re looking for another successful predicting year in 2014.

This season I will try to include predictions for more of the markets. Painstaking entry of past lines shows that line betting gives at least the same returns as head-to-head betting. LOOK AT THIS PLOT!

profit-start2014So keep an eye on the blog this week. I will try to have predictions out in a timely manner each week. And please email me with any questions!

“Keep an eye on it”