The past week or so has been pretty rough for Celtic goalkeeper Joe Hart.

After failing to cover himself in glory as Celtic went down 2-0 to Dutch champions Feyenoord in the Champions League last Tuesday, the former England number one was then shown a red card in the Hoops’ win at Livingston on Saturday. His dismissal in West Lothian - after coming off his line and wiping out Livingston’s Mo Sangare 15 minutes before half-time - didn’t cost Celtic on the day, with the 10 men going on to secure a 3-0 win.

Both matches highlighted a worrying decline in Hart’s performance level though, and his role in Feyenoord’s opener in Rotterdam - coming in added on time of a first half where Celtic had impressed - was certainly costly. Let's break down his part in that goal in De Kuip first, and take a look at his performance data in the Champions League.

There were of course some other mitigating factors in the concession of the opening goal last Tuesday night in the Netherlands that should be factored in, Kyogo’s placement on the inside of the wall was the first problem. However, this can already be partially levelled at Hart, given his responsibility to set the wall. Kyogo’s decision to then turn his back as Calvin Stengs strikes the ball - a fundamental error at any level let alone the Champions League - has to be laid solely at the Japanese striker’s door.

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Parking the issues with the wall, Hart essentially had a strike from 30-plus yards to deal with. Even without a wall, this should have taken a special strike to beat a Champions League-level goalkeeper from that distance.

Although Hart would not have been expecting his wall to break in front of him, Stengs’ shot was not anywhere near the corner or side of the net and the ball also bounced on its way towards the goal. This should have given a quick and agile goalkeeper sufficient time to get across and push the ball around the post, but Hart was slow to get across and only able to help it into the net.

As Ryan McGinlay highlighted in the StatsBomb match report, the data provider gave the initial shot a value of just 0.03 xG with the Post-Shot xG, which takes into account what happens to the shot once the ball has then left a player’s boot, i.e. how well it was struck, where on the goal it is likely to end up, etc. Still, it had a relatively low 0.13 xG.

Hart, of course, deserves some credit for his penalty save later in the game - although it has to be said it wasn’t the best penalty kick ever taken - and he could not be faulted for Feyenoord’s second.  Considering the quality of all the shots he faced in Rotterdam coldly exposes the issue with Hart at the Champions League though.

StatsBomb recorded that he only faced a total Post-Shot xG 0.40, the sixth lowest of all goalkeepers in the opening round of fixtures in the competition. Conceding twice from this value of Post-Shot xG gave Hart the lowest Goals Saved Above Average (how many goals did the keeper save/concede versus expectation) score of -1.60, the lowest of any goalkeeper on matchday one. Only Manchester United’s Andre Onana - who endured a torrid night in Munich - came close with -1.55. The next lowest was -0.62.

Hart didn’t fare much better with the ball at his feet last midweek. His Goalkeeper On-Ball Value (OBV), the goalkeeper-specific version of a metric designed by StatsBomb to measure the value of each event objectively and quantitatively on the pitch, was the fourth lowest (-0.82) of all goalkeepers over the first two nights of the group stage.

Admittedly just a one-game sample, these numbers are down on Hart’s average in the Champions League last season when he recorded -0.12 Goals Saved Above Average per 90 and -0.24 Goalkeeper OBV per 90.

It, therefore, seems safe to say that Hart’s performances haven’t exactly had a positive impact on the team’s chances on Europe’s biggest stage, not last season or in the opening match this season where he has showed signs of further decline at this level.

With Celtic often at a disadvantage before a ball is kicked quality-wise, against most Champions League opponents, success on this stage has been dependent on having a goalkeeper capable of making several top saves. For example, think of Artur Boruc against Manchester United, Fraser Forster against Barcelona, and more recently Lazio. As we probably knew before the season started, Hart is simply not capable of those positive game-defining performances. Simply put, his status as first-choice goalkeeper considerably impacts what Celtic can achieve in Europe this season.

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Hart’s week then went from bad to worse last week when he only lasted just half an hour of Celtic’s lunchtime trip to the Tony Macaroni Arena. Slow off of his line, Hart misjudged the bounce of a long ball, albeit on a difficult surface, before crashing into the Livingston forward. There could be no complaints about referee John Beaton’s decision to brandish what was remarkably Hart’s first-ever red card in his career.

The SPFL Premiership is of course a much more forgiving environment, evidenced by Celtic’s ability to still overcome their opponent at the weekend despite a numerical disadvantage. In general, before his red card at Livingston, Hart had appeared to enjoy a fairly steady start to the league campaign, too, leaving Ibrox with a clean sheet in the first derby, and making a few decent stops in other early domestic games. What does the data say about his current performance domestic level though?

Still dealing with a relatively small sample size of 5.8 90s, a radar comparing his league numbers so far this season to last season’s Premiership campaign (shown below) can shed more light on Hart’s domestic performances and whether a decline there could be costly this season.

Here, we can see Hart’s Goalkeeper OBV has so far improved somewhat on last season, -0.04 compared to -0.17 last season. However, in other key areas, it appears, so far anyway, that Hart is declining in a domestic sense too. His Positioning Error rate, Shot-Stopping % and Goals Saved Above Average (GSAA) are all down on last season, albeit only by a small margin at this stage.

The previously mentioned GSAA metric is particularly key when it comes to measuring one of the most fundamental goalkeeping attributes, shot stopping. A greater positive figure indicates that more saves have been made by the keeper beyond the anticipated average, whereas a negative value suggests that more goals are being conceded compared to what would been expected from an ‘average’ goalkeeper.

Tracking this specific metric over Hart’s full Celtic career further highlights his decline and points to a potential issue at the domestic level now, too. In his first season - 2022/23 - Hart’s GSAA was just -0.03 per 90. So, throughout that season, Hart only gave up over one goal more than he should have. His intangible qualities of leadership and experience, which were particularly important in the first season under Ange Postecoglou, probably did mitigate any slight performance deficiencies there.

Last season, he declined slightly though, to -0.08 per 90. Given ‘Angeball 2.0’ blew every domestic opponent away, it mattered little in terms of the bigger picture.

As mentioned Hart’s GSAA is only down slightly (-0.09 per 90) so far in 23/24, but it is down. Although only a slight decline, given the increased uncertainty this season with a new manager still imprinting his philosophy on the squad, and a lot of change in the defence due to injuries, this could be more of an issue and it could well result in the concession of an additional two, perhaps even three goals than would be expected from an ‘average’ keeper.

This still might not sound like a huge amount for a team as dominant as Celtic tends to be domestically but shaken out over a season, that could still have the potential to translate into turning one or two wins into draws or a draw into a defeat. That’s before you consider he may decline further, in terms of his speed and agility, as the season goes on.

Given the evidence, Celtic’s decision to persist with the now 36-year-old Hart, already well beyond the peak years for a goalkeeper (believed to be 27-29, according to research by The Athletic), for another season was an unnecessary risk.

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Of course, there are hundreds of other factors at play in a 38-game league campaign too but controlling as many of the variables as you can always be a priority, no matter how dominant you have been before. With the resources at the club’s disposal, much publicised in recent days following the release of the annual accounts, and some evidence of Hart’s continued decline already there, a goalkeeper that would have represented a reasonable upgrade could have, and should have, been a priority.  

Loosely linked with Croatia’s World Cup goalkeeper, Dominik Livakovic, there just didn’t seem to be a serious appetite from the club to upgrade the goalkeeper department in Rodgers’ first window back in the Parkhead manager’s office, though.

Out of contract at the end of the season, it does seem unlikely that Hart will continue beyond 23/24 as Celtic’s number one. Beyond that, Liverpool’s Caoimhin Kelleher has, since the window closed, been suggested as a future Celtic target for the position.

In the shorter term, only next May will we know whether the risk of sticking with the former Manchester City keeper has ultimately turned out to be a ‘season-defining’ one.