Fair warning: Depending on your personal affinities, the following exercise may be either painful, hilarious or offensive. OK, now let's quickly go through all of the once-in-a-lifetime incidents that happened in last year's Champions League final between Liverpool and Real Madrid.
First, Mohamed Salah, he of the 44 goals and 16 assists in his debut season with Liverpool, badly injured his shoulder after a (pick your adjective of choice) collision with Sergio Ramos. He was subbed off in tears after just 30 minutes. In the first half-hour, Liverpool outshot Madrid 9-2; after Salah left, the balance shifted to 12-4 in Madrid's favor over the final hour.
Then, in the 51st minute, Liverpool keeper Loris Karius collected an over-hit through ball and proceeded to throw the ball directly into Karim Benzema's foot, seeing it deflect in to make it 1-0. After Sadio Mane evened the score in the 55th minute, Gareth Bale was subbed on with half-an-hour to go. Three minutes later, he scored on a contorted bicycle kick from the top of the penalty area. Bale scored again in the 83rd minute with a harmless-looking shot from 35 yards out hit right at the chest of Karius, who proceeded to aimlessly push the ball into his own net.
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From Liverpool's point of view, there's not much to be done about a game like that; it's a matter of volatility. You can't budget against your best player getting injured in the most important game of the season, and Real Madrid are Real Madrid because they have a player like Gareth Bale, who has decided multiple cup finals all by himself, sitting on the bench. Shake your fists at the soccer gods and then move on. Oh, and get yourself a new goalkeeper.
A year after the debacle in Kiev, Liverpool are back in the Champions League final. This time, they're favorites and this time, it's not despite the guy in goal. No, they're here because of him.
Last summer, Liverpool shattered the transfer fee for a goalkeeper when they brought in Alisson from Roma for £56.25 million. (It was then broken weeks later when Chelsea bought Kepa from Athletic Bilbao for £72m.) For a squad that had been mostly built on undervalued players, this seemed to mark a change in the way Liverpool did things... or, perhaps it wasn't.
"He maybe added one-third of the points that Liverpool gained this season," said Paul Power, an analyst with the data company STATS. "You know, it's chicken feed, basically, what they paid for him."
Goalkeepers have long been a frustrating puzzle for decision-makers, coaches and talent evaluators alike. As Statsbomb's Derrick Yam wrote in a paper for this year's Sloan Sports Analytics Conference: "A goalkeeper in the England Premier League faces only 12 shots a game, 80 percent of which miss the goal frame completely or were blocked before they reach the goalkeeper. It's not uncommon for a goalkeeper to go an entire game without making one save."
On top of the scarcity of events, there's an issue of context. The style of defense a team plays will affect the type and total of shots they allow. Stopping shots for Burnley -- a side that concedes a ton of chances but tries to keep as many men behind the ball as possible -- is a vastly different exercise than stopping shots for Liverpool, a team that doesn't allow many shots but has fewer bodies back in defense whenever they do. Traditional numbers like "clean sheets" or "save percentage" don't account for these effects, and they also don't account for the quality of the finish.
All of these moving parts seem to show up in just how little clubs seem to value the players they put in goal. Before Liverpool's deal for Alisson, the world-record fee for a keeper was Juventus's £47.6m transfer for Parma's Gianluigi Buffon... in 2001. Among the 50 most expensive transfers ever, just three are keepers. Ederson, the fourth-most expensive shot-stopper, cost less than "punchline players" like Paulinho, Andy Carroll and Shkodran Mustafi, whose high fees have paid more for comedy than competence.
Power, however, is working to change how keepers are assessed and, in turn, how they're valued. At STATS, he helped create a model that uses artificial intelligence to determine what each keeper's specific skills actually are. As he put it: "What's his ability to come off his line? What's his ability to make his body big? Is he better at shots to his feet or hands, or both?"
With that information, they're able to determine how likely a specific keeper is to save a specific shot. The model can then simulate how each keeper in the Premier League would have fared against every single shot taken across the competition that season: a useful way to compare the performance of players up and down the table. It can also help give a sense of how a keeper's performance would translate across the unique shot profiles that each team concedes.
According to the model, Alisson was the best keeper in England this year, and he was the ideal fit for Liverpool's defense. The 26-year-old Brazilian saved 0.31 goals per game more than the average keeper would have. Despite a late-season swoon, Manchester United's David De Gea was second at 0.27.
"In the 2017-18 season, when Liverpool conceded shots, the shots were very dangerous," said Power. "So Liverpool needed a goalkeeper who was able to cope in one-on-one situations where the defense just completely collapsed and the keeper had to do something amazing. Alisson's true strengths were that he was able to make these kind of superhuman saves. He would have saved at least seven goals that [Simon] Mignolet or Karius would have conceded."
A goal is worth around one point and Liverpool improved by 22 points from last year to this year, but Alisson's impact wasn't just limited to domestic play. In the final Champions League group stage game against Napoli, with Liverpool up 1-0 in a game they had to win in order to qualify for the knockout round, he made a point-blank save to deny Arkadiusz Milik in the 89th minute.
"There aren't many keepers who could have done that," said Power. "There are maybe seven or eight in the world."
After the four-goal Champions League semifinal comeback against Barcelona at Anfield, much of the focus was on the fact that unheralded squad players Divock Origi and Georginio Wijnaldum each scored twice, or that Trent Alexander-Arnold's quick corner won the game, or that Barcelona collapsed, dramatically, for the second time in as many years. But none of that matters if Alisson doesn't pitch a shutout and Barcelona get an away goal. He made five saves, including two on "big chances," which the data company Opta defines as a "situation where a player should reasonably be expected to score."
Alisson's counterpart on Saturday in Madrid will be Tottenham's Hugo Lloris, who also rates highly in the STATS system. He saved the fourth-most goals above average (0.21 per game) in the Premier League this season.
"In terms of actually picking out shots into the corners, Lloris is exceptional," Power said. "Where he sometimes gets caught are shots that are actually straight at him. He compensates for shots that go through him by being able to reach these really high-probability shots that should be goals."
Of course, an inability to save shots directly at a keeper was partially responsible for Liverpool's demise against Madrid last season. The acquisition of Alisson solved that problem, and then some.
If there's another bicycle kick into the top corner, Alisson is at least more likely to tip it wide than either of his predecessors. And if there's another early injury to a key player -- well, could he nurse his teammate back to health? We can't say for sure; the model doesn't account for that yet.