Expected goals (known as ‘xG’) measures the quality of a shot calculated using several variables such as shot angle, assist type and distance from goal. Expected goals can prove whether a shor or header was defined as a big chance.
How can this stat be used to improve analysis and football predictions? Let’s see the terminology and then analyse in more depth the expected goals statistic.
Expected Goals terminology
- Expected goals (xG) – the number of goals a player or team is expected to score based on the quality and quantity of shots they take.
- Expected goals per 90 (xG/90) – the number of goals a player is expected to score in 90 minutes.
- Expected goals for (xGf) – the number of goals a team is expected to score based on the quality and quantity of shots they take.
- Expected goals against (xGa) – the number of goals a team is expected to concede based on the quality and quantity of shots the opponents take.
- Non-penalty expected goals (npxG) – the number of goals expected without including penalties.
- Expected points (xPts) – the number of points a team is expected to win based on xG statistics.
- Expected goals assisted (xA) – the number of assists a player is expected to make based on the quality and quantity of the shots his teammated take directly from his passes.
Example: Expected Goals explained
Expected Goals is a stat/metric which assesses the chance of a shot or header eding as a goal. It is a good way to determine the quality of a shot. As a simple example, a shot with a 0.5 expected goals (xG) value should be scored 50% of the times. An expected goal of 1 is the highest value possible, meaning the player has a 100% chance of scoring.
These chances are usually the ones ‘on the line’ or when you hear the commentator screaming “How did he miss that???”
What factors are used to calculate expected goals?
There are different Expected Goals models used by the big data companies analysing the number game of football. It is not really clear which one is the most accurate since there is always some bias that has todo with the quality of a team or a player that changes the balance of the specific stat.
There are some basic factors that everyone agrees, like the location of the shot. This takes the biggest part of a shot’s xG rating. In more detail the factors that everyone agrees on:
- Distance from goal.
- Angle of the shot.
- Shot or header.
- Was the player marked closely?
- The quality of the assist (low or high cross, cut-through ball, long ball, etc).
- Open play or set piece (direct free-kick or corner kick).
- Is it a rebound?
- Has the player just beaten an opponent?
Hold on a minute, there is more. Think of this. A player is at the penalty spot receiving a low cross. In this case, the body position of the attacker as well as the positions of defenders, the direction of the body while taking the shot, the attack speed and where the first possession of the attack started are factors that could evaluate the expected goals.
Not to mention the quality and skill level of the player receiving the ball. It is not the same if Lewandovski or a League One forward is the receiver, right?
To wrap this up, It is not a simple model for you (or us) to make, but we can take the advantage of using this data correctly in betting.
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How to use Expected Goals in football betting
As mentioned above, the Expected Goals offer an extremely useful measure for analysis, but they do not always reflect 100% real situations. It is important in football betting to take into account outliers such as the individual quality of a striker’s finishing, the strength of a defense or the motivation of a team to win a specific game as well as other factors.
Expected goals in a betting context that can help identify outliers that can bring value in the future. Barcelona looked like struggling during the first half of the season 2020-2021 in La Liga, but their expected goals and expected points were double than what they were actually showing. That meant that the quality was there but other factors were taking over. They still sit behind Atletico Madrid and might not win the title, but in this case the numbers said the truth!
Cases like this could provide potential value if the market did not consider the abnormal nature of the team’s short-term results.
- View also our guide on Live Betting.