Expected goals: Quantifying Sporting’s attack

Sporting scored 68 goals last season compared to Benfica’s 72 and Porto’s 71 which isn’t bad at all. But goals don’t tell us the full story as after all, they are very unpredictable events. Sometimes a shot nestles in the top corner from 40 yards out while on other occasions seemingly unmissable chances are hit well over the crossbar. The better team or striker doesn’t always score more goals, but they do tend to revert to the mean level of performance over a lengthy period of time. The process of creating numerous good quality chances and conceding few is what ultimately produces long term success. This is where expected goals (xG) can help us quantify a team’s performance with good reliability. Essentially xG models assign a probability rating to each shot depending on numerous variables such as shot location, assist type and much more. This creates a useful measure of chance quality.

What is clearly seen in the subsequent visualisations is the lack of support for Bas Dost with all Sporting’s other attackers hovering around the measly 0.2 xG/90 mark. This was strikingly different to both Benfica and Porto who’s attack offered numerous consistent goal threats.

Bas Dost: Is his form sustainable?

As mentioned before, Bas Dost scored a mammoth 50% of Sporting’s goals in the league. By forming a probability distribution chart we can clearly see that given the chance quality (xG) of Bas Dost’s shots, he was most likely to score just 16 non-penalty goals. The chance of him netting the 27 non-penalty goals he scored last season was under 0.5%.

Devin Pleuler showed in this fantastic article that the correlation between scoring goals above expected from one year to the next was almost nothing. Although Bas Dost is probably a better finisher than the average player and likely to outperform expected goals, this analysis still puts doubt over his ability to score more than expected this time around. Goals tend to revert to the expected mean and variance means Dost could go the other way possibly even underperforming this time around. With Dost highly unlikely to score this many goals again, where do the goals come from that push Sporting past Benfica and Porto going to come from?

It may be the case that Sporting create more chances for Dost this time around. Acuña is an accurate passer that is stylistically a crosser of the ball and probably a better fit for Dost than Bryan Ruiz on the left. Gelson is also a more traditional wide player and can be expected to do even better this season at just 22 years of age. Bruno Fernandes will bring a creative spark to the middle of the pitch and improve the delivery to Dost too. But Dost over performed so spectacularly last season that even if Sporting do create much better chances this time around he is unlikely to produce the same output in terms of goals.

Gelson, Bruno Fernandes, Acuña and Doumbia: Can they lift the burden on Dost?

Despite scoring 13 league goals already this season the underlying performances are still not quite as good with Sporting overperforming in 78% of simulations. Sporting have managed to improve their output from 1.80 xG/game to 2.12 xG/game this season and although immediate signs are positive, the sample is small and the question is whether this improved output is sustainable.

Bruno Fernandes never really looked a goalscorer in Italy with 0.21 non-penalty goals/90 with Acuña hitting identical numbers in Argentina. Gelson has a better 0.41 xG/90 but the sample is small and he hit just 0.2 xG/90 last season; although at 22 he’s still young and potentially improving on the goalscoring front. In truth only new signing Doumbia has shown any real consistent goalscoring ability throughout his career with an impressive 0.84 non-penalty goals/90. However, he’s played nearly all his career at a level below the top Portuguese division and question marks remain over whether his style of play is suited to facing the deep block defences common in Portugal. He’s also not really an option alongside Dost which reduces the collective goalscoring threat that Sporting can field in the same line up. These moderate numbers and concerns over Doumbia do raise the question of whether Sporting’s improved xG output per game is sustainable going forward.

The reason Dost and Doumbia are unsuitable as partners is because they are poachers in style who stay high up the pitch away from build-up. Playing the two together up front would mean a lack presence between the opposition defence and midfield lines, potentially leading to insufficient options in the central areas to progress the ball. This commonly leads to the ball being played wide as a means to progress play and can force a team into a predictable crossing game. Therefore it’s not much of a surprise that Jorge Jesus has kept them apart during pre-season and hasn’t really looked at integrating them together at all thus far. On top of that Doumbia is most effective on the offensive transition when the ball is won high up the pitch in open games. Sporting rarely face this sort of game outside of European competition so there has to be doubts over whether he can produce what is required from Sporting as a lone striker on a consistent basis.

Summer transfer window: Could Sporting have done things differently?

Jorge Jesus’ move to a more rigid 4–2–3–1 has put increased emphasis on the striker for goals. This is a risky strategy especially when Dost overperformed so spectacularly in that role last season as and is highly unlikely to provide such a high number of goals again. New signing Doumbia just doesn’t seem like an ideal fit stylistically to take over from Dost if needed and isn’t really suited to playing alongside him either. Maybe Gelson can step up this season as his early performances have suggested but again the sample is small and it’s debatable if he can sustain this over the season considering his previous form in front of goal.

I do find it strange that Sporting haven’t paid more attention to the unsustainable nature of Bas Dost’s form. Perhaps analytics isn’t a big part of their operation but for me the logical thing would have been to look for someone who can play outwide and also as a second striker. This would give Sporting a lot of tactical flexibility, a bigger collective threat in front of goal, lift the pressure on Dost and Bruno Fernandes could drop seamlessly back into the number 8 role anyway. Maybe a deal couldn’t be made with this type of player but I find that hard to believe when Sporting have such good connections in South America while Gabriel Barbosa also made a loan move over the summer to rivals Benfica.

Conclusion

In the end despite considerable improvements defensively and numerous additions going forward I can’t help but think Sporting have made a mistake by not signing a forward who can play behind the striker or offer a real goal threat outwide. With Dost unlikely to provide the same output and no definite answers to replacing this, Sporting might just fall short of the title again this season.

Acknowledgements

This article was written with the aid of StrataData, which is property of Stratagem Technologies (www.stratagem.co). StrataData powers the StrataBet Sports Trading Platform (www.stratabet.com), in addition to StrataBet Premium Recommendations (https://stratatips.co/recommendations.html).

All simulations were performed using Danny Page’s Season Simulator (http://dannypage.github.io/).