If you have looked online to read about football anytime in the last couple years, you will surely have kept bumping into this xG thing. “What is it?” and “Is there even any use to it?” are some of the many questions that may come to you when you keep coming across this stat. I will try and answer those queries for you. Firstly, xG is a model that predicts the chance that each and every shot taken in a game is converted into a goal. xG stands for ‘Expected Goals’. A score is given to each and every single shot taken, representing the likelihood it ends up in the back of the net. It takes into account numerous factors in deciding the quality of a chance. So a shot from near the penalty spot will have a much higher xG value than that of one from near the halfway line. The xG value does not alter depending on the player taking the chance, however it can be used to determine if a player is performing sustainably, or whether he’s likely going through an extreme purple patch. It can also be used to assess where a team should be in the table based on the quality of chances created, compared to where they actually lie in the division. We recently had Soccer Saturday host Jeff Stelling call xG “the most useless stat in the history of football”, however the proof is in the pudding with more football clubs and analysts using the stat to help them achieve their goals.
xA is a very similar statistic to xG, in that it is a model that predicts the likelihood of an event occurring based on historical factors. In this case, xA is ‘Expected Assists’. It measures the probability that a given pass will become a goal assist. It takes into consideration the type of pass, where the pass ended up and the length of the pass. We can then add up a player or team’s expected assists to give us an idea of the number of assists a specific player or team should have based on their attacking play and build up.
‘Key Pass’ is a phrase bandied around a lot, especially when we talk about creative players such as Pogba and de Bruyne. Though it is sometimes used loosely, it’s recognised definition is ‘the final pass leading to the recipient of the ball having an attempt on goal’. This can be used to help identify creative players who are skilled at often picking out players in shooting opportunities.
“How did he miss that, I could’ve scored that!” is something I am sure every single football fan has exclaimed at one point as they fall to their knees in front of the TV, watching as a player on their team misses a 6 yard shot. When a player is presented with one of these opportunities, it is known as a clear chance. A clear chance is defined as ‘a situation where a player should be reasonably expected to score usually in a one-on-one scenario or from very close range’. This metric can be used in various ways. Firstly, it can be used to identify which players create the most clear chances on the pitch, telling us who the best creators are for their teams. It can also be used to show us which players are better at finishing their clear chances; some players struggle much more than others putting away clear chances.
PPDA (Passes Allowed per Defensive Action)
You may or may not have come across the acronym PPDA before. Whether this term is vaguely familiar to you or never seen before, I will try and help to clear the fog around it. PPDA is calculated by the ‘number of passes made by attacking team / number of defensive actions’, usually both figures are calculated with reference to a specific area of the pitch. The smaller the PPDA value, the greater the level of defensive intensity; the defence has allowed a lower ratio of uncontested passes to be completed. It is not completely indicative of how good a team is at pressing, some teams only press at certain times when a trigger has occurred, some constantly press the position of the ball. However the stat can provide an objective measurement to how much a team is pressing the opposition.
Progressive Passes or Runs
Progressive passes and runs identify actions which advance the ball 10 or more yards in attack, or into the 18-yard-box. A successful progressive pass or run doubles the likelihood that the attacking team will score within the next seven seconds, on average.
Post-Shot Expected Goals
A relatively new statistic, it is used to help see how effective a goalkeeper is at shot-stopping. It is similar to xG, it is the calculation of the quality of shots on target and seeing what chance, on average, that shot has of being scored based on the quality of the chance. Then we can see if a goalkeeper is out or under-performing as expected.