Or Where did expected goals come from? The term ‘expected goals’ appeared in a paper about ice hockey performance presented by Brian Macdonald at the MIT Sloan Sports Analytics Conference in 2012 Brian’s method for calculating expected goals was reported in the paper: We used data from the last four full NHL seasons
How much xG is a penalty? The probabilities range between 0 and 1 A shot of 01 xG means a shot like this should be scored 10% of the time A shot of 08 xG means a shot like this should be scored 80% of the time A penalty xG value is fixed to 076
Ainsi, What is xG and xGA? xG numbers tend to be vastly inflated when a team is playing against ten men, whereas xGA, which measures the quality of chances conceded, can be altered by enforced defensive upheaval
What is xG and xA?
xA, or expected assists, is the xG which follows a pass that assists a shot This indicates a player’s ability to set up scoring chances without having to rely on the actual result of the shot or the shooter’s luck/ability Note: Because xA comes from passes, not all assists will be given an xA value
How reliable is xG? xG gives us a more accurate way of predicting match outcomes than by simply using individual stats In the Premier League, only 716% of teams that had the most shots won the fixture, while close to 81% of teams that obtain a higher xG score win games
How accurate is xG? An accuracy of 905% sounds pretty good at first, but we need to bring this into the context of our data The shot/goal data is a highly class-imbalanced data set, meaning that there is a significant disparity between the number of positive (goal) and negative labels (no goal)
When did xG become popular? Since xG was introduced in 2012 by Opta’s Sam Green , the metric has gone on to become one of the most widespread and insightful within football analytics
How much xG is a big chance?
For big chances (xG over 033), small number of shots are recorded and convergence may not happen Here is a histogram of the number of shots taken and goals scored We can see how most shots amass less than 005xG, and how the number of big chances decreases drastically
When was xG invented? Since xG was introduced in 2012 by Opta’s Sam Green , the metric has gone on to become one of the most widespread and insightful within football analytics
How is xG expected goals calculated?
How is Expected Goals calculated? It is calculated by comparing it to thousands of shots recorded earlier based on factors such as distance, position of defenders, type and speed of pass, type of shot, shot angles and various other aspects
What is xG build up? The spirit of xG Build up is based on knowing which players are part of passing chains that end in a shot but without taking into account the last two links – shot and last pass -, thus measuring midfielders, centre-backs or full-backs who have an important influence on their team’s possessions