One of the first columns I wrote for The Celtic Way examined the specific requirements of playing the keeper position at the club and how Ange Postecoglou’s track record of goalkeeper deployment in Japan offered additional dynamics.

The column was penned and published prior to the signing of Joe Hart. We are now approaching two full seasons of performance data that offer context to revisit and grade my analysis, as well as Hart’s quality and fit with 'Ange-ball'.

Here was how I framed the analysis at the time:

Postecoglou’s use of the keeping position is not conventional and, in fact, I believe Celtic are facing a situation in the upcoming season in which a below-average shot-stopper could still be a better fit for Ange’s system.

StatsBomb announced an upgrade to their data capture and associated modeling last May but the scale of the task to update all historical data across all the leagues they have covered resulted in the update just being completed earlier this month.

Part of this upgrade had a material impact on goalkeeper analysis, as legacy xG-related models across public data vendors had not quantified the impact of shot velocity. 

For example, two players could have taken shots from identical positions on the pitch with opposition keepers standing at similar locations in front of the goalmouth and models from Wyscout, Opta, or other providers would assign the same post-shot xG model values regardless of whether the shot was a screamer or a mishit lobbed comfortably into the hands of the keeper. StatsBomb’s models now incorporate relative characterisations for the velocity of each shot.

While shot stopping remains a hugely important component of keeper play, with StatsBomb’s latest update offering top-notch data to measure, other aspects such as sweeping, positioning, claims and parries all contribute as well. 

With that explanation out of the way, here is a radar comparing Hart’s two league campaigns through Sunday’s game at Kilmarnock:

The importance of this comparison is the concept of benchmarking Hart’s performance level against Scottish Premiership-level opposition relative to all cup and league competitions covered by StatsBomb. In theory, you’d expect to see a Celtic player dominate in important metrics versus domestic competition in order to have a reasonable expectation that their quality will translate to European competitions.

Here are Hart’s two group stage performance levels in Europe:

The usual caveat about small sample sizes certainly applies to that report but the metrics conform with what is a reasonable expectation: that a player performing at around an average level in the SPFL is more likely than not to struggle against higher-quality opposition in Europa League and Champions League group stages.

As we dig deeper into the specific metrics for Hart, we see that a basic premise from that July 2021 column has been proved wrong: Postecoglou has not deployed Hart in anywhere near the aggressive sweeper-keeper role he asked of his custodians while in Japan. The best guess is that the manager made a wise decision to pivot from asking Hart to fill such a role after seeing his limitations in mobility and on-ball skills. 

We can see from the first report above that Hart’s OBV metrics for passing, dribbling and carrying benchmarked poorly in both seasons despite high volumes of actions.

For example, during the current league campaign, Hart’s 17.50 average carries have been in the 72th percentile, while dribble and carry OBV is in just the second percentile. With Hart offering relatively low levels of value from non-shot-stopping aspects of keeper play, it is a requirement for his shot-stopping to be excellent in order for him to outperform his peer group.

As we can see, that has unfortunately not been the case at the league level – and basically fell apart when trying to step up to the higher levels in Europe. 

The broader goalkeeper OBV metric also offered context on Hart’s performance levels and the following radar may be a bit surprising to many:

The report shows Hart’s tenure at Celtic in league games compared to Vasilis Barkas’ period as being mostly the primary number one at Celtic, which was through the February 2021 draw away to Livingston.

As was likely not a surprise to supporters, we see from the shot-stopping metric that Barkas was quite poor over that period. However, despite that drag on his overall performance levels, he basically matched Hart’s level for goalkeeper OBV during his tenure to date. 

When I penned the column in July 2021, my appreciation for the dynamics and relative dominance of a Postecoglou-managed Celtic side over league opposition was lacking.

As I have written over the past year, these competitive dynamics have squashed the chance creation of all non-Rangers opponents to bare-bones levels. It could be argued that the dominance has been so persistent and pervasive that Celtic would likely have been successful at a comparable degree whether Scott Bain, Benjamin Siegrist or Hart has been the first-choice keeper. 

While the prior column focused upon what at that time was a campaign to reclaim the league title amidst severe uncertainty, my analytical focus has shifted more and more towards how Celtic may be able to better compete in Europe.

While intangibles most certainly play a role on the margins, as we saw with Scott Brown and the 2020-21 season, Father Time waits for no person. With Hart already performing at what is arguably an insufficient standard to compete in playing Postecoglou’s desired style in Europe, his reliance on shot-stopping to offer value increases his ageing curve-related risks. 

A cautionary tale in this regard has been the last three league campaigns for Rangers’ primary number one, Allan McGregor. This radar was a comparison of McGregor’s 2020-21 league season with Hart’s current one:

McGregor had an excellent 2020-21 season in shot-stopping and we can see from the radar the outsized impact that had on his goalkeeper OBV despite the other mobility and sweeping-related metrics benchmarking mediocre to poor.

As he has aged and his shot-stopping value has swung from a big strength to this season has been very poor, his overall value has imploded to be one of the worst across all keepers covered by StatsBomb.

While Hart has a few years on McGregor and has turned 36 this week, his tenure at Celtic and immediately preceding campaigns elsewhere have not suggested a level of shot-stopping skill from which to absorb some normal age-based decline heading into next season.

With his performance levels in Europe already having been insufficient, combined with deficiencies in the various other aspects of keeper play, Celtic should make upgrading the position a priority with an eye towards next season’s continental campaign.

For some additional perspective, one of this season’s surprise clubs in the Champions League group stage was Club Brugge. The Belgians were able to qualify for the knockout stage in a group with Porto, Bayer Leverkusen and Atletico Madrid. This radar compares broad performance metrics for Celtic with Brugge:

The two sides conceded average amounts of xG that were not significantly different, while Celtic was far more successful in creating chances in attack.

However, there was a material difference between the two sides relative to the quality of keeper play. Here is a comparison of Hart with Simon Mignolet:

We can see the huge disparity in performance levels, which contributed to Celtic conceding 2.50 goals per game versus 0.67 by Club Brugge.

This highlights the paradox for Celtic: a keeper who is a good enough shot-stopper for Europe will have almost nothing to do outside of at least six group-stage Champions League and derby games. 

Celtic keepers regularly face fewer than two shots on target per game on average domestically.

Is it realistic to expect the Hoops to upgrade enough in midfield and defence to make a material dent in the 2.50 goals conceded per game in each of the group-stage campaigns of the past two seasons playing Postecogolou’s aggressive style of play?

Despite potential challenges in attracting keeper talent, replacing Hart with a quantifiable upgrade should be a top recruitment priority this summer if Celtic are to significantly improve results in Europe next season.