Stoke’s GK coach explains how clubs use data to assess goalkeepers

In Depth

It is notoriously difficult to assess goalkeepers using statistics – but Stoke‘s goalkeeping coach Andy Quy says clubs are still finding ways of using data to identify strengths and weaknesses in their custodians. 

The position of goalkeeper and what is required from those who occupy it is probably the least understood by fans and pundits. So in the absence of technical know-how, the simplest way to judge is from statistics. Goalkeeping by numbers.

The oldest and most accessible metric is clean sheets. A keeper who doesn’t concede goals must be doing his job, right? Then came save percentages, followed by more and more nuanced save percentages.

But save success rates consider none of the variables a goalkeeper must contend with in almost every action they perform as a shot-stopper. From what distance is the attempt made? From what angle? Opposed or unopposed?

One improved model comes in the form of expected goals (xG) which assesses the quality of chances, but even then it doesn’t account for the position of the goalkeeper or his defenders, or who was taking the shot – deadly centre-forward or lumbering centre-back?

In short, goalkeeping statistics should certainly be taken with a fistful of salt, especially when presented in isolation.

That does not mean, however, that such data is dismissed by those within the game.

Andy Quy, first-team goalkeeping coach at Stoke City for more than a decade, uses statistics to see if there is anything the naked eye might be missing.

“I won’t look at the stats on a day-to-day basis,” Quy says. “But over a period of time, perhaps six to 10 games, we might try to build a picture, whether that be individually with the goalkeepers or within units of the team.

“Defensively, we’ll see what is happening in the games and break those down into what areas of the pitch the shots have come from. Crosses, too.

“But you have to give yourself a period of time to assess what those numbers mean. It’s difficult from a goalkeeping perspective to read too much into one game, but we might identify a trend over a period of time, whether it be a strength or a weakness.”

Quy says his keepers, who currently include Jack Butland, Shay Given and Lee Grant, are “very receptive” to listening to what the data may be telling them.

For example, over recent seasons, statistics suggested goalkeepers were having more success saving shots from distance by staying closer to their line, therefore allowing more reaction time, rather than moving down the line of the ball to narrow the angles the shooter has to aim at.

“Playing deeper in the goal for shots around the 18-yard box – that’s something we’ve changed a lot over the last two years,” Quy says.

“We have to build up the data over a period of time and make it work to our advantage, but that’s definitely an area in which which the stats have made a difference to our methods.

“It’s something Shay has looked at in the two years he’s been here and he’s altered his start position accordingly, which demonstrates that you’re never too old to learn.”

Spotting stars

Performance analysis is not the only area of Quy’s role where data proves useful.

“I can’t get to all the games that I need to see everyone, so there’s a definite use for the statistics within the recruitment process,” he says. “We can look at certain criteria that we’d want,

“Height was an attribute that has often been put forward by the managers I’ve worked under. Tony Pulis wanted a goalkeeper that was of a good size, someone with a good strike who could kick the ball a decent distance but with good accuracy. That’s obviously something quite easy to measure.

“Once we’ve got that raw data, we break it down and put it together with what we might see on a video.

“That process might sometimes throw up the odd gem or anomaly that might not be at a fashionable club or in a fashionable country.

“We’ve got a good team of scouts and they feed back keepers that they’ve seen wherever they might be. But we can’t cover every game everywhere so there’s a good case for using statistics to start that process.”

It is not just goalkeeping but the defensive side of the game as a whole in which the analytics community is looking for more reliable and accurate metrics. Defensive actions are generally reactive, whereas those in possession control and dictate the play, therefore making their contribution easier to record and measure.

Changing metrics

As Guardiola’s desire to recruit Claudio Bravo and release Joe Hart illustrates, the attacking side of goalkeeping is more of a consideration for managers than ever before. This is one area in which Quy mines the data to measure how his keepers are working within the team.

“At Stoke, the priority has always been that we need a keeper who will keep the ball out of the net. But now the game dictates that we need to be better at building play up and be more confident on the ball. I think we’ve definitely gone that way.

“The team that we had when we were first promoted, there’s no doubt about it, we were a direct team. But we were successful doing that. We had players in the side and goalkeepers that could put the ball into good areas where we could be successful.

“Over the last three or four years, with Asmir Begovic, Jack Butland and Lee Grant, we’ve been more comfortable on the ball at the back. With the defenders we’ve got, we’ve been able to play a more possession-based game and move the ball more comfortably.

“We look at the videos every day, constantly analysing training – are there things that can be improved or changed?

“Post-game also, we’ll sit down with the keepers for probably 45 minutes, seeing how it played out for them.

“We’ll look at some of the numbers – how many contacts with the ball, long kicks, short passes, whether or not they were successful – but, crucially, we have to put that in context of the game.”

And that’s the key to goalkeeping analysis – context.

It might not be convenient when so many use only a headline or a shareable graphic before rushing to their judgement, but the art of goalkeeping is far too nuanced and sophisticated to be assessed by numbers alone.

By Ian Watson


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