Expected Goals (xG) are turning into one of the most important metrics in modern football. Used to determine which side had the better chances of scoring during an individual football match, xG stats give us a fairly good idea of who should have won based on their opportunities.
Expected Goals are calculated by measuring the likelihood of a shot ending up in a goal. This takes into account factors such as the angle from which the shot was taken, the goalkeeper’s positioning, the speed of the pass before the shot and the type of shot itself.
In Celtic’s 1-0 win against Aberdeen on Wednesday, Neil Lennon’s side accumulated an xG of 1.34, while Aberdeen’s was 0.63; this was a fairly neat representation of how xG stats can work. In other games, things aren’t always so simple. In January’s most recent Old Firm match, Celtic should technically have won with an xG of 1.44 (Rangers’ was 0.62) but the Gers came out on top. In this scenario, Celtic underperformed their xG.
There are some limitations to xG stats. They don’t, for example, take own goals into account. Winning a penalty automatically increases your xG by 0.76, so you could technically create no chances all match but have an impressive xG of 1.52 if you happen to draw two fouls in the opponent’s box.
Overall, however, Expected Goals are a very useful metric for understanding how well sides are performing in both the attacking third and their defensive area – we can measure Expected Goals Against (xGA) as well. By using these stats, we can calculate Expected Points and see how a league table would look if all teams took their chances and kept out the shots they’d be expected to.
From the two examples used above, Celtic should have won both games and therefore had an Expected Points total of six. However, they lost to Rangers and therefore only attained three actual points – they therefore underperformed their Expected Points by three over the course of those two matches.
By using these stats, we can see what the Scottish Premiership table would look like if all teams got the results their stats suggest they should. Would many teams move up or down the table? Who are overperforming on their Expected Points, and which teams are underperforming? I’ve analysed the answers to those questions here.
Below is an image of what the Premiership table looks like in terms of actual points. Rangers are runaway leaders at the top with 79 points, ahead of Celtic in second (64 points). Dundee United are battling with St Mirren for the final top six spot, while Kilmarnock, Hamilton Accies and Ross County are embroiled in a relegation tussle at the bottom.
If teams had attained their expected points, the table would look as it is below. Bear in mind that, for the most part, Expected Goals stats don’t bring about draws – so the majority of teams here have significantly higher tallys than they actually would. However, it gives us a good indication of which teams deserve their current league standings and which ones (perhaps) don’t.
St Johnstone 51
St Mirren 34
Hamilton Accies 28
Dundee United 24
Ross County 15
As you can see, there would be a number of significant changes. For the most part, teams in Scotland are underperforming when it comes to their points totals. St Johnstone, without a shadow of a doubt, lead the pack in this avenue.
Callum Davidson’s side currently have 30 points, just seven clear of bottom spot having played a game more than Ross County. If they had matched their xG and xGA tallys, they would have 51 points – a swing of 21. A gulf this size cannot be underestimated; the Saints would be joint-fourth with Livingston and would have effectively wrapped up a top half finish by now. They would be three points in front of Aberdeen, who have fifteen more than them in actual points. Instead, they’ve failed to capitalise on matches they’ve dominated and loiter in the bottom half.
Aberdeen’s situation would become even more worrying for fans. Pressure is already mounting on manager Derek McInnes after a six-game winless streak, but they’d be even worse off if Expected Points were the chosen metric for league standings. While they are technically underperforming by three points, they would slip to sixth in the league standings; this means they are actually performing worse than Aberdeen fans may even realise. With underlying numbers this poor, time looks to be running out for McInnes.
Neil Lennon and Celtic will be cursing their luck. Their bid for ten titles in a row has looked to be over for a long time now, but it would still be well and truly on if they had won the games they were expected to. They would be just six points behind city rivals Rangers with two Old Firm matches to come, but instead remain fifteen points worse off and with just one more chance at a trophy this season.
The biggest overperformers this season have been Micky Mellon’s Dundee United. They currently sit seventh in the table – a very respectable spot considering this is their first season back in the top flight. The stats, however, suggest they are lucky to be in such a position. Their Expected Points are just 24 (ten lower than their actual 34) and had they not managed to grind out a league-high ten draws, they would find themselves in tenth position – joint with Accies in the relegation playoff spot. They’ll need to keep overperforming if they are to maintain their current position.
Ross County have exceeded expectations as well. The Dingwall side are bottom of the table anyway, but are still within touching distance of safety – if they had matched their Expected Points, they would be nine points adrift. They’ll need to keep punching above their weight if they are to have a chance of survival; County went on a run of twenty matches with zero Expected Points earlier this campaign, but managed to collect twelve.
Ex-Livingston manager Gary Holt will have been cursing his luck in the weeks leading up to his resignation. During his final fifteen games in charge, Livi collected 24 Expected Points. However, they were unlucky enough to accumulate a mere twelve actual points during this period. It looks like a combination of poor finishing and dodgy defending may have cost Holt his job, because his side were generally outperforming the opposition in terms of quality chances created.
Just two teams have matched their Expected Points totals; St Mirren on 34 and Kilmarnock on 24. This tells us that both of these sides pretty much deserve to be where they are in the table – good for the Paisley side, but not such positive news for new Killie boss Tommy Wright.
There are limitations to using Expected Goals and Expected Points in football analytics, but the pros outweigh the cons. By using them here, we can determine which sides might expect a surge in results during the closing stages of the season, and which may experience a drop-off in form. Whatever the case, we’re in for an exhilarating conclusion to the Premiership season.
*Statistics are correct as of 20/02/21.
Featured image credit: Sky Sports