Expected Data: the Dominant Football Statistic

Expected data (xG, xPts, xA, xGA) has been part of the footballing statistics world for over a decade now, helping fans understand their teams' performance on a higher level. As one of the most common forms of simple analysis in the modern game, expected data has been criticised at times with claims it does not show the ‘real picture’ of a football game, making teams look better/worse than they actually were at times.

How do expected points, goals and assists work?

Expected goals (xG) is an accumulated total that factors in each shot on target a team has. Every strike is measured in a system that scores it from 0-1 on the likelihood of the attempt becoming a goal. Opta, for example, has a database of over one million shots that have each been calculated over the years by data scientists. The factors behind each score given include the distance, angle, goalkeeper and other players' positions, pressure from opposing defenders, shot type and pattern of play.

Expected assists (xA) are similar, but instead, look at the likelihood that a pass will be a primary assist. Aspects of a pass that will be factored in are the finishing location of the pass and what type of pass it was. This model is not reliant on whether a shot was taken from this pass, so it credits all passes, regardless of whether they result in a shot.

The statistic-obsessed era of football continues to create more types of expected data, some other included expected goals against (xGA) and post-shot expected goals (PSxG) for goalkeeping metrics. The ultimate combination is expected points (xPts), with each team given a total based on xG, the probabilities of the outcome of each match they have played, performance analysis and strategic insights. This leaves us with a ‘justice table’ ranking every team by their expected points.

The Premier League’s expected points table for the 2024/25 season can vary depending on the website selected. Using Opta’s (the company that ignited football’s ‘expected’ obsession) table as an example, Liverpool still come out on top, and the actual bottom three still face a comfortable relegation, yet it is some of the teams in between that cause a few shocks…

Bournemouth

It is no secret that the Cherries have an outstanding season and still have a strong possibility of qualifying for Europe with four games to go. Bournemouth are 10th and a point from 8th, but their expected points sees them rise to 4th, ahead of Manchester City, Newcastle and Aston Villa. This indicates that Andoni Iraola’s side have underperformed expectations, their smooth style of football setting statistical expectations that exceed their actual points tally.

Nottingham Forest

Forest provide the other big shock on the list, but unlike Bournemouth, they will be glad that the expected points do not reflect the real table. The Reds will be able to seal a return to European football this weekend after three decades without UEFA action at the City Ground. Sitting in 6th with four games to go, Nottingham Forest are still in the mix for a top-three finish, and winning their game in hand would pull them above Chelsea, Newcastle and Manchester City. The expected points table places them in 14th with 43.9 expected points, over 16 digits below Forest’s actual total.

Nuno Espirito Santo’s side have notably got an extremely low expected goals for (xGF) compared to their top seven counterparts, highlighting that Forest have been more clinical in front of goal than the shots they took suggested.

Newcastle

The final team that makes a big jump in the expected points charts (albeit in the wrong direction) is Newcastle United, who fall from 3rd to 6th. A small mid-season dip left them in 12th for part of December, but since then, they have won 13 of their 17 Premier League games, reestablishing themselves in the European spots.

It is an easy misconception that expected stats are based on expectations. The name originates from the mathematical concept of ‘expected value’ meaning that the data focuses on probability over reality.

To answer the question, expected points can actually be a better way of judging how a team will perform compared to stats like expected goals, as they consider more than simply efforts on goal. Despite that, the metric should not be taken completely seriously though, as sport is often full of surprises and nothing can be determined by probability.

All statistics in this article are taken from Opta.com