A brief overview of Salah's record-breaking 2017-18 season

When Salah came back to the Premier League in 2017 after a failed first stint at Chelsea, many fans were sceptical. By the end of the season, Salah had broken the record for goals scored in a single campaign with 32 and had carried Liverpool to the Champion's League final. Yet, many fans were not convinced labelling him a "one-season wonder". A couple of years on, Salah has finally silenced his critics by consistently performing since. Let's take a look at exactly how good Salah was during his first season with Liverpool.

We are using data from Wyscout. The table below suggests there is some missing matches given Salah scored 32 goals that season and Kane 30. Despite this, we can still carry out analysis with the data available.

Top 10 Goal-Scorers - 2017-18 Premier League Season

Him and Kane are the two outstanding goal-scorers with 31 and 27 goals respectively. Both of them are by far the players that attempted the most shots, though their goal to shot ratio and proportion of shots on target is similar to the other players. Hence, Salah's many goals seems to be a consequence of him shooting often rather than him being a more accurate or clinical finisher.

Salah playing as a winger makes his scoring record all the more impressive. Though the likes of Ronaldo and Messi have made us accustomed to wingers being prolific goal-scorers. The more typical strikers such as Aguero and Kane have a variety of weapons in their arsenal - right foot, left foot, header - their shots are evenly distributed. With Salah, not so much... 136 shots taken: 114 with his left foot. As the plot below shows, his goals mostly follow the same profile - he cuts on his left from the wing and slots it in the opposite corner.

Salah's shots and goals (filled red circles) during the 2017-18 season

His goals mostly all came from inside the area. So Salah may have shot more than other players but he also made sure to shoot from dangerous positions. In fact, although he scored a couple of wonder-goals, many were pretty unspectacular finishes. This is what is required to break scoring records - a blend of having many shots and being effective. We have seen that Salah had the high rate of shooting. What about the effectiveness ?

We can use the expected goals model to measure this effectiveness and assess how many goals we would have expected him to score. A simple expected goals model based only on the angle and his distance from the goal as well as whether the shot is a header gives him an xG of 17. Hence, if Salah had been your average player, from his 136 shots, he would have been expected to only score 17 goals. Yet he scored 31. Well, Salah is apparently not your average player, nor are the other top 10 scorers. All of these players scored more goals than what we could have expected given their shots.

Expected Goals (xG) of top 10 Goal-Scorers

The goal to xG ratio is a measure of how clinical a player is relative to the average player. During the 17-18 season, Salah was extremely clinical and really scored more goals than perhaps he should have given the opportunities he had. Indeed, over the following seasons, he maintained his levels of performance but unsurprisingly, these resulted in more reasonable goal-scoring numbers. Maintaining that level of efficiency is hard and it is already quite impressive that he managed to, over a whole season.

Let's look at a visual representation of Salah's effectiveness that year. The following plot is the probability of scoring when shooting from various areas of the pitch for the average player.

This is what the same plot looks like but when the Salah of 17/18 is taking the shot:

This really summarises the incredible season Salah had and how ruthless and effective he was in front of goal.

Note that this last plot was made from an xG model fitted only on Salah's shot. It is interesting to look at in this context but comes from a small amount of data available (136 shots).