Expected goals: A key stat for football betting

Few sports remain untouched by statistical analysis in the modern era. US sports, such as baseball and its dedicated sabermetricians, continue to set the benchmark, but others are increasingly catching up.

Included among the pursuits now drowning in data is the most popular sport on the planet. Football, the beautiful game, or the global game, is firmly under the microscope of the mathematicians.

The days of football bettors relying solely on hunches are long gone. These days, fans of the best football betting sites have a wealth of data at their disposal. From the Premier League to the FIFA World Cup, many stats vie for our attention. However, the stat that is increasingly winning the race for relevance is that of Expected Goals or xG for short.

What is expected goals?

Expected goals is the subject of much debate, match analysis data, and is regularly featured in betting article collections, but what exactly is it?

At the end of any football game, we can clearly see how many goals a team has actually scored – it is shown on the scoreboard. However, whilst it is the only measure that counts, the scoreboard is not always the most accurate reflection of how well, or how poorly, a team has played. Perhaps the winning team scored on their only venture into the opposition box, while the losing side repeatedly rattled the woodwork and found the opponent’s goalkeeper in world-beating form.

Expected goals help us look beyond the bare result and present a picture of how well each team played on the day. Rather than actual goals, expected goals tell us how many goals a team would be expected to score given the quality of the chances they created.

The expected goals calculation

When calculating expected goals, every shot in a game is assigned a value between 0 and 1. A 0 value indicates that the shot had no chance of resulting in a goal, something akin to an overhead kick from 70 yards, for example. A value of 1 suggests a certain goal, i.e. a tap-in on the goal line. Values in between represent the percentage chance that the shot would result in a goal, e.g. an xG of 0.5 indicates a 50% chance.

The xG values are calculated by analysing thousands of shots from all areas of the pitch and how often they resulted in a goal. As with many things in the realms of data analysis, the xG formula is long and complicated, but it aims to take the following common-sense factors into account.

• Distance – The greater the distance from the goal, the lower the xG.
• Angle – Shots taken from a tighter angle have a lower xG.
• Body Part – If distance and angle are equal, a shot taken with a foot is more likely to result in a goal than a header.
• Circumstances – Shots teed up by a dribble or through ball have a higher xG than those following a cross.
• Defenders – The closer the nearest defender is to the player taking the shot, the lower the xG.

A team’s total xG in a match is simply the combination of the xG values of each of their individual shots.

xG against, meanwhile, shows how many goals we would expect a team to have conceded given the quality of chances created by their opponents.

xG betting pointers

Any stat which helps present a fuller picture of how well a team is playing is worth factoring into your betting process. xG is particularly useful when analysing the following markets:

• Match results: Teams whose results are better than their xG performance can be worth taking on. Likewise, sides that are struggling for results but are performing to a high xG level may present a betting opportunity.
• Total goals: When looking at the recent results of the sides, it can be easy to follow the trend. For example, if the past six games of a team have featured under 2.5 goals, it can be tempting to back under 2.5 goals again. However, actual goals aren’t always a reflection of attacking output. Analysing the xG stats may identify a counterintuitive value bet.

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