Football is in a constant state of evolution. The game has changed an incredible amount in a relatively short space of time, with teams today striving to push the limits and the boundaries of performance.
To reach new heights, clubs are using advanced software tools to generate detailed analytics and data reports. Something we’ve seen really come to the fore in recent times is the concept of expected goals. This can sound a little strange at first, how can we possibly quantify how many goals a team is expected to score? Let’s find out.
What do We Mean By Expected Goals?
The expected goals metric is expressed as xG. You’ll have likely seen this used in post-match reports on social media and on TV, it’s become one of the most popular stats used by coaches and fans alike as performances are picked over in detail after the fact.
Expected goals assesses goal-scoring chances that take place in a game and how likely it is that these chances are scored. It can be used to measure the expected goals of the team as a whole or for individual players, making it a particularly useful tool when evaluating performances.
How Does Expected Goals Work?
Expected goals can seem like a rather vague, woolly concept, and it has faced criticism from pundits who believe it doesn’t tell the full story. However, it’s becoming an increasingly important tool for analysts, and we’re seeing it used by major clubs when evaluating performances and optimising training routines.
Expected goals can also influence football betting odds, and has become a key tool used by gambling firms looking to predict match outcomes.
How does the expected goals metric actually work? It analyses a number of factors to give a percentage-based numerical rating. For example, if a player takes a shot from the edge of the box, the expected goals rating for the opportunity could read as 0.25xG. What this means is that this opportunity should result in a goal 25% of the time.
What Factors Does Expected Goals Analyse?
To generate the percentage rating, expected goals takes a number of factors into account when analysing a goal-scoring opportunity.
The first of these is the assist that led to the opportunity; the quality and type of which can influence the resultant rating. The second is whether the attempt was made using the player’s foot or their head. Third, the quality of the chance is taken into account, big chances will generate higher ratings. Angle and distance play important roles too.
These are the primary factors used by expected goals to generate ratings. However, there are other metrics used by the system, such as whether opportunities came from open play or set-pieces and whether defenders were attempting to stop the shot.
How is Expected Goals Used
In the past, analysts relied on metrics just as attempted shots and shots on target. While these are still important when it comes to post-match evaluations, they don’t paint the full picture.
For example, a strike from 35 yards that goes over the bar and a missed open goal from 5 yards out will both be labelled as shots on target, despite the obvious differences between them.
What expected goals does is allow coaches to dive deeper into the quality of goal-scoring chances and gain more insights into player and team performance. If the number of goals scored is less than the xG rating, this could indicate a problem. Conversely, if the number of goals scored is higher than the xG, this suggests that the team or individual is performing particularly well.
Conclusion
The concept of expected goals is relatively new in the world of football analysis, but it’s quickly becoming one of the most critical metrics and we can certainly expect to see it used more and more as football looks to further focus on stats.
