We all know it is not always the best team that wins in football. In order to prove this theory, we performed a detailed analysis using advanced statistics.
If the team that attacks and shoots the most does not always collect the three points, how many times does this happen and how can it affect the outcomes during the season?
Through algorithms we have calculated various aspects of the Serie A teams. In this way, we can better understand the nature of the game that these teams develop on the pitch and what are the weaknesses and strengths of each of them.
To do so we used the xG (Expected Goals), a value that expresses the offensive danger of a team and that can tell us how many goals it should have scored according to the number of shots and their danger. The level of danger is determined by the conversion rates of the goals scored. They vary from the type of shot and the place from where the shot is triggered. Scoring from a distance is much less likely than from the small area.
From the intersection of these data, we can understand the danger value of each shot. For example, it is definitely more difficult to shoot from 35 meters than from 20. The same concept is true if a shot comes from outside the area or from the center.
In short, the xG highlighs the possibility for a team to score and the value is simply calculated by the sum of the various percentages. For example, with two shots from the small area, a team collects a xG of about 0.74 (or 73.4% probability). Of course the data does not only depend on the area where the shot is triggered and the tactical situation. Often it also depends on the player’s individual quality.
The xG data also measures other values, such as the skill of the goalkeeper or the defensive strength of a team. If two teams have the same defensive xG value (the expected goal in their own goal), but they have suffered a different number of goals, this leads us to consider the solidity and efficiency of a defense line. For examle, if a defensive line is lined up in a proper way, it is going to be more difficult for the opponents to score. Here are the “meritocratic” results calculated for week 35.
On this day of the championship we can see how often a team finishes more than normal (Lazio) or it cannot capitalize on the opportunities created (Juventus had several chances to score in the derby but it wasn’t able to finalize).
A different result than the one expected by the xG in a single match may depend on the goalkeeper or on the good performance of the strikers.
Over the course of a whole season we can also understand what has had a decisive impact on the results (finalization, goalkeeper and xG creation).
The team that creates more xG (expected goals) is Roma, while the one that suffers less on the pitch is Juventus. However the question is this…How is it possible that Napoli scored more goals than Roma but its xG is lower?
This naturally leads us to discover a different value, the efficiency of the game (which is divided into offensive and defensive).
Offensive efficiency can be explained as the finalization phase of a team. It’s often triggered by the attackers’ individual abilities and the tactical type of attack put in place. For example, statistically a counterattack leads to the goal much more easily than a shot against a defense properly positioned).
Defensive efficiency refers to the position and the ability of a defender to deflect a shot, to the proper positioning of the entire defensive line, and to the skills of the goalkeeper.
According to the chart above, Juventus’ values are excellent. In fact, it is a team that finalizes its offensive phase and defends properly. This is due to the high qualities of the players on its roster. Almost the same thing is true for Roma. The Giallorossi suffer a bit more than the Bianconeri, but thanks to the quality of its defenders (Fazio played a great season so far) and the ability of its keeper (Szczesny’s performances were remarkable) it suffers less goals than expected (xG).
Another thing to note is Napoli’s lack of defensive efficiency. Sarri’s crew creates many chances to score but it’s too easy for its opponents to score goals.
Noteworthy is Cagliari’s great offensive efficiency. In fact, thanks to its offensive phase and the goals scored, the team comfortably avoided the relegation. Instead, Empoli based its season on the defensive phase.