You may have seen us refer to Expected Goals (xG) in our event pages and in game statistics/scoreboards on site. We have started to include this to give you extra information around how a team or player has previously performed, or are currently performing. This can give a better indicator of past performance than a teams results which you could find useful at the point of placing a bet.
What is Expected Goals (xG)?
Expected goals (xG) determines the quality of a scoring opportunity. Each chance is given a probability of being scored. The higher the probability, the better the chance. Watch the video below for an example and more information.
How is Expected Goals (xG) calculated?
Not all attempts on target have the same likelihood of successfully ending up in the net.
A shot is more likely to be scored than a header from the same position on the field, for example and shot location and shot type are the two major contributing factors when projecting how likely it is that a goal is scored from any chance.
Minor contributing factors include how the chance originated. For instance it is taken into consideration whether the opportunity followed a fast break, there was a slower build up or if it was created from a set piece.
xG, is expressed in terms of probability. For example, penalty kicks are typically converted around 78% of the time. So prior to the kick a penalty would have an expected goals figure of 0.78.
Therefore, xG figures lie between 0 and 1, where 0 means that a goal will never be scored from such a chance and 1 indicates total certainty.
In reality, the figures will range from very small, in the region of 0.01 for speculative long shots up to 0.6 when a shot is taken from relatively close range.
The xG figures are created from the outcome of shots that have been taken from the same sort of area in the past (e.g. were those shots usually blocked, did they miss or go in etc).
xG is calculated from a large dataset of historic matches and these data models are then validated using sample data that was not part of the original model building. So if a shot was given an xG of 0.30 (a 30 % chance of going in), the samples are used to see if that was the case when applied outside of the collected data.
How to use Expected Goals (xG)
Football is a low scoring sport, where most top flight leagues average around 2.5 total goals per game and by looking at the process of chance creation, denoted by the expected goals of each individual chance, it is possible to more quickly identify those teams who are profiting from an unsustainable lucky, hot streak.
The volume of chances created or faced by a side is often a better indicator of future performance than the outcome as it relates to the teams performance. The thought process being that if a team plays well over a long period, positive results are more likely to happen in future than negative ones.
At its most simplistic, the expected goals created by each team in a match can be summed and compared to the actual result to determine whether or not the match outcome was a fair reflection of what had happened.
The versatility of xG can be further extended to individual players, to evaluate their scoring record.