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Introducing Total Shots Ratio – And How It Transfers To The A-League

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Advanced stats and analytics are becoming exceedingly crucial to running professional sporting organisations, and New Zealand is firmly behind the eight ball.

While the American sporting scene features hundreds of columnists and front-office personnel willing to break down the finest statistical analysis on offer for their major sports, New Zealand has externally struggled to get beyond the cliché-ridden logic that blissfully plagues some of the most popular commentary on our favourite sports.

Some major sporting organisations in Aotearoa are well on the ball in regards to statistical revolution, but (generally speaking) the rest of the population lags behind, with the internal data collected by the various sporting teams never being seen outside of the squad environment.

In football terms, while I’m fairly sure the All Whites and the Wellington Phoenix have plenty of statistical data on their hands to work with (Cynical observers may disagree with me), that is where it ends, as the hard-working media men and women are paid to write previews, recaps and player profiles instead of digging into archived information to collate a stat which the majority of their readers will care little about.

Here’s the good news – I don’t get paid! So I have free reign to write about whatever I want, and as such, I’m going to be providing a look at some of the advanced statistics which are dominant in world football, and whether they can be applied successfully to the A-League.

Because the A-League is a fairly strange league in the context of world football, not all the statistics so popular in other areas of the world will translate effectively down under. But regardless, I hope to either educate, entertain, or for a last resort, enrage.

The statistic I was most intrigued to spotlight – and one you, the good reader, may have seen before – is a concept called “Total Shots Ratio”.

Total Shots Ratio is, as expected, the ratio of how many shots a team takes versus the number of total shots. The equation: Shots for/(shots for + shots against) is a simple way of categorising how frequently a team shoots compared to their opponents.

For example if a contest between the Phoenix and the Perth Glory contained 30 shots, with the Phoenix shooting 20 times, the Nix’s TSR would be 20/30 or 0.67, with Perth recording a value of 10/30 or 0.33.

Why is this important? Well, as you know – goals are very rare in football, and the fact that they can be scored in such a varied range of ways creates a situation where a team’s prior scoring record isn’t a particularly valuable way to predict future goals.

That’s where TSR comes in. By evaluating how often a side will score goals, you must first calculate how often they do the thing which leads to scoring goals, which is shooting, while conversely denying their opponents opportunities to shoot at goal.

You’ve probably already stumbled across the logic point missing here – not all shots are created equal. That is indeed correct, and is the biggest flaw in the TSR statistic, as teams who prefer to try their luck from distance can be boosted when compared to sides that wait patiently for a glorious chance before shooting (Arsenal, looking at you).

In the short term, Total Shot Ratio holds little bearing, due to the fact that match outcomes can be so variable, with long-ball defensive sides often nicking points against dominant opposition.

However, in the long term, research pinned that the points accumulated by a side is definitely correlated with their TSR, with the graph below showing how over a large period of time, TSR becomes increasingly correlated with outcomes.

tsr graph

(In James Grayson’s graph, black represents the title winners, blue represents the teams that qualified for the champions league and red represents teams that were relegated.)

Additionally, mid-term TSR values show a very strong relationship to the TSR recorded by a team at the end of the season, while teams which underperformed relative to their Total Shot Ratio have in many cases proven to bounce back the season after.

So, with all that in mind, which teams does TSR pin as the most dominant in the A-League? And does the A-League’s relative talent disparity and often-heavy roster turnover make season-by-season projections irrelevant?

I went through all the available shooting data from last season and compiled each team’s Total Shot Ratio. (The available shot data is slightly off here or there, but that’s the A-League for you)

1st: Western Sydney Wanderers: 0.548 (League Finish: Second)

2nd: Melbourne Heart: 0.53 (LF: 10th)

3rd: Adelaide United: 0.529 (LF: 6th)

4th: Newcastle Jets: 0.518 (LF: 7th)

5th: Brisbane Roar: 0.515 (LF: 1st)

6th: Wellington Phoenix: 0.495 (LF: 9th)

7th: Sydney FC: 0.48 (LF: 5th)

8th: Melbourne Victory: 0.469 (LF: 4th)

9th: Central Coast Mariners: 0.458 (LF: 3rd)

10th: Perth Glory: 0.42 (LF: 8th)

So, not much of a correlation there between TSR and final league placing. Wanderers proved they were deserving of their high finish and Perth showed how they were probably the worst team in the league last season, regardless of their finish (Eighth).

The biggest reason likely behind the lack of a distinct correlation is the short A-League season (At least compared to the big European counterparts), creating a more random and far smaller sample size in which to collate data from.

So does this season showcase as an outlier, or is the stat simply irrelevant?

TSR’s proven track record makes it a stat worth keeping an eye on this season, both in predictive value (Will the Heart and Adelaide improve at the expense of the Mariners?), and in-season performance (Checking in at the halfway point).

 

Categories: A-League

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Niall Anderson

Hamilton raised, Niall Anderson now halves his time between university studies in Auckland and catching up on all things Waikato football in the Tron. Having covered Waikato FC and WaiBOP United in the ASB Premiership, Niall is also the lead writer at nzhoops.co.nz. Find him on Twitter @NiallGunner.

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