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Big Al loves stats

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November 14, 2018
How Are Kepa and Alisson Settling in England?

By Grace Robertson


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This summer, Liverpool shocked the footballing world by not just breaking but smashing the transfer record for a goalkeeper that had stood since 2001. Then Chelsea broke it again less than a month later.
One was bought to fix a long term weakness in the side, the other needed to replace a departing former Golden Glove winner. Alisson Becker and Kepa Arrizabalaga have become the two most expensive goalkeepers in the history of football. By a lot. As such, it’s not unreasonable to judge them both by very high standards.
Alisson Becker

Liverpool are at this point well known for incorporating data into their recruitment, so it would hardly be a surprise to know that Alisson has shown up well in a lot of metrics. While StatsBomb’s new goalkeeping data has not yet recorded last season’s Serie A games, his performances for Roma did earn him praise from some existing goalkeeping models, with Colin Trainor and Mark Taylor both highlighting him as a standout. StatsBomb did record data for the World Cup, but the number of chances he faced (1.57 post-shot xG, from which he conceded 2 goals) were so few as to tell us almost nothing about his abilities.
While the price tag made expectations very high, Alisson’s predecessors in a Liverpool shirt did the exact opposite. Of the 20 “first choice” goalkeepers in the Premier League last season, Simon Mignolet’s shot stopping is rated as the 19th best. While the model estimates that the average keeper “should” have saved 68.4% of the shots Mignolet faced, the Belgian only managed 61.4%, a goals saved above average percentage of -7.0% only beaten by Joe Hart at the negative end of the scale. He can hardly complain that he was dropped halfway through the season, and while Karius did offer an improvement, he was only saving at around an average rate which, combined with a disastrous Champions League final, saw him get the hook as well.
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As for Alisson, it seems to be so far, so good for the Brazilian. Thus far in the Premier League, he has saved 2.48 more goals than one would expect from the average goalkeeper, or 0.19 per 90. Alisson has surely benefited from a much less chaotic Liverpool defence this season, with the average keeper being expected to save 75.1% of the shots he has faced so far. Liverpool have made sure that the average chance Alisson faces is the second easiest of any keeper in the Premier League this year, but he has still beaten expectations with a save percentage of 83.3%, and a goals saved above average percentage of 8.3%. Had Mignolet been playing (and performing as he did last year), the model estimates that Liverpool would have conceded around 9.25 goals. That Jurgen Klopp’s men have only let in 5 shows the value Alisson adds over the current number two.
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It’s worth pointing out that Alisson has still only faced 29 shots on target. If he is able to maintain his current form over a full season then he will have surely justified his price tag, though this remains an open question. The information that exists about Alisson’s previous performances, and Liverpool’s reputation for incorporating analytics into recruitment, suggests that the expectations should be high, though, and his shot stopping performances so far have matched what one might expect from a £65 million goalkeeper.
Of course, it is not merely his shot stopping that has earned Alisson such a reputation. His ability with his feet has been lauded and highlighted, earning him the reputation of a “modern” goalkeeper who is able to kick it as well as save it. On this front, it is also mostly as one would expect. Alisson’s raw passing completion percentage of 80% remains slightly shy of league leaders Kepa and Ederson, though he is playing passes about 12% longer than the Chelsea and Man City keepers on average. Where he really shines with his feet, though, is when we incorporate StatsBomb’s pressure data. His passing accuracy under pressure of 73% is the best in the Premier League, despite four other starting keepers playing it shorter in these situations. He is only seeing a 7% drop in his completion under pressure, while Ederson and Kepa are seeing a 15% and 19% decrease, respectively. This might be a key aspect of why Liverpool wanted him so badly. It’s well known at this point how Klopp likes to invite the opposition to press his side at strategic moments before being able to launch a counter attack. If Liverpool can invite the press onto Alisson while he is able to stay calm and still play the pass he wants, this helps open up spaces higher up the pitch as the opponent moves forward to press the keeper only to find themselves easily bypassed. If this is worth a few goals a year, then Alisson’s value is even greater than that which his shot stopping brings.
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29 shots is not enough to draw any conclusion on. But regardless, Alisson has been very good thus far when i've seen him
 
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