Rangers' goalkeeping performance assessed - Joshua Barrie

"I won’t be strengthening the goalkeeper position next month,” he said speaking at his press conference before last week’s trip to Dingwall.

"Allan McGregor has saved this club time and time again. Jon McLaughlin at the start of the season did very well. Made a mistake in a high-profile game, but I trust him. Robby [McCrorie] moving forward, he knows I've got a lot of faith in him. In the last month before leaving here, he played away at Alashkert and at home against Celtic and was excellent in both games, I believe man of the match in probably both games.

"We're in a healthy place. I do get it, when the ball goes in, everyone looks at the goalkeeper. I trust all the keepers here and I have a lot of faith in them."

So, what do the numbers say about Rangers’ goalkeeping performance in the league this season?

After all, Beale spoke just last week about not “coming back and being romantic” with members of the previous squad, adding: “This is about trying to build a new Rangers and the cornerstone of that has to be young players”.

To assess the performance of goalkeepers we can use StatsBomb’s Goals Saved Above Average (GSAA) metric. Defined as: “How many goals did the keeper save/concede versus expectation (Post-Shot xG faced)? This is representative of how many goals the goalkeeper's saves prevented within a season.”

This doesn’t consider every aspect of a keeper’s performance. There are other angles to analyse such as their contribution on the ball, sweeping actions and ability to claim high balls.

However, most people would agree that shot-stopping is a No.1's priority and over the course of this campaign, Rangers have lagged behind in this area.

Per 90, only Carljohan Eriksson has a worse GSAA rating than McGregor and McLaughlin.

Over the course of the season, StatsBomb measures McGregor’s GSAA to be -4.29.

And McLaughlin’s at -2.25.

Goalkeeping analysis is arguably the most specialised area within the industry. How can we know if a keeper should’ve saved a shot or not? What’s the line between an excellent shot and poor positioning? Especially if so few have experience of the position.

On a pure shot-stopping basis, GSAA offers a reliable barometer. StatsBomb's advanced data uses details such as optimal goalkeeper positioning, the location of attackers and defenders as well as shot impact and height. This means GSAA can accurately define how many goals a goalkeeper's saves prevent over the course of a season.

Rangers’ win in Aberdeen last week provides helpful contrasting examples. Let’s start with the equaliser.

StatsBomb’s freezeframe shows us three important details in Lopes' goal. The xG (expected goal) of the chance, the PSxG (Post-Shot expected goal) of the shot and the optimal position of the goalkeeper.

xG is a metric that measures the probability of a shot resulting in a goal. PSxG uses information after that shot has been taken to re-evaluate the chance, such as shot velocity, goalkeeper positioning and proximity of defenders.

Simply speaking, a big difference between xG and PSxG probably means the keeper couldn’t have saved the goal. A small difference means they should’ve done better.

Lopes’ goal was an example of the latter, with an xG of 0.08 and PSxG of 0.10. McGregor starts too far to his right, appears to not trust his wall by taking a step left and then sees the ball loop over his initial starting position. According to the data, it's a goal you'd expect him to save.

Leighton Clarkson’s strike in the second half was different. It had an xG of 0.06 but PSxG of 0.70. Given the shot’s velocity and swerve it simply ends up out of reach quickly, despite McGregor being optimally positioned.

Looking at McGregor’s GSAA map, all the shots on target faced this season, the key at the bottom of the graphic offers important context. The darker the shot, the higher quality and chance of a goal.

Arguably, McGregor’s ‘preventable goals’ haven’t actually cost many points, because of when they’ve occurred. A full list of goals conceded, PSxG and results are found below.

• Liam Smith, Rangers 2-1 Dundee United, PSxG 0.17
• Connor Barron, Rangers 4-1 Aberdeen, PSxG 0.73
• Joel Nouble, Rangers 1-1 Livingston, PSxG 0.85
• James Brown, St Johnstone 2-1 Rangers, PSxG 0.13
• Nicky Clark, St Johnstone 2-1 Rangers, PSxG 0.83
• Jonah Ayunga, St Mirren 1-1 Rangers, PSxG 0.92
• Ryan Porteous, Rangers 3-2 Hibs, PSxG 0.24
• Kevin Nisbet, Rangers 3-2 Hibs, PSxG 0.44
• Luis Lopez, Aberdeen 2-3 Rangers, PSxG 0.10
• Leighton Clarkson, Aberdeen 2-3 Rangers, 0.70

Why does this matter? As we can see, only ‘preventable’ concessions against St Johnstone cost points. Ayunga’s goal in the draw with St Mirren had an impact on the result, as Rangers dropped points, but wasn’t ‘preventable’ given its high PSxG value.

Other ‘preventable’ concessions, Lopes and Smith’s goals, didn’t stop Rangers from securing three points.

Let’s apply the same methodology for McLaughlin. His numerous high-profile mistakes in the Old Firm defeat earlier this season are analysed in greater detail here. A full list of goals conceded, PSxG and results are found below.

• Joel Nouble, Livingston 1-2 Rangers, PSxG 0.47
• Martin Boyle, Hibs 2-2 Rangers, PSxG 0.72
• Josh Campbell, Hibs 2-2 Rangers, PSxG 0.75
• Liel Abada, Celtic 4-0 Rangers, PSxG 0.76
• Jota, Celtic 4-0 Rangers, PSxG 0.29
• Liel Abada, Celtic 4-0 Rangers, PSxG 0.63
• David Turnbull, Celtic 4-0 Rangers, PSxG 0.19

The most ‘preventable’ concession, Turnbull’s goal, compounded a disastrous day but again, it’s hard to place a binary judgement on the overall GSAA number because of when that goal arrived, and the relatively small number of matches he has played.

Last season, McGregor’s mistakes against Hearts in a 1-1 draw, Ross County in a 3-3 draw, Motherwell in a 2-2 draw and either Old Firm defeat proved costly.

That had a direct result on points and that could be the case again this season unless the veteran enjoys a purple patch as was the case at points last season.

Beale will have to hope that whoever starts in goals over the second half of the season performs to a consistently higher standard. While goalkeeping errors haven't cost many points this season, goalkeeping performance leaves room for improvement.