For better or for worse, Celtic’s on-field relationship with Joe Hart will come to an end this Sunday at the national stadium, as he hangs up his gloves after a glittering career in association football.

An unlikely partnership lasting just under three years, the veteran goalkeeper was signed from Tottenham Hotspur under Ange Postecoglou, who looked to fill a gaping hole in the Celtic defence after the collective struggles of Vasilis Barkas, Scott Bain and Conor Hazard the season prior.

The former England international was effectively a journeyman prior to his move up north to Celtic, with spells at Torino, Burnley, West Ham and Spurs all proving to be fruitless in a pursuit to recapture his previous form found at Manchester City. Hart needed a career refresh, and Celtic offered him the opportunity to do just that.

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Three seasons later, the 37-year-old will be looking to secure his seventh major honour at the club, after clinching his third league title in as many seasons last week against Kilmarnock, lifting the trophy on Saturday afternoon. One of the many success stories under Postecoglou, Hart has been a calming presence for the majority of his Celtic career, though he has not been without his faults, especially at the start of this current campaign.

Ever since the announcement of his retirement on February 22, there is a general and accepted consensus that Hart has played some of his best football in a Celtic jersey during this period. Using StatsBomb radars, we put that hypothesis to the test, as the influential number one calls time on an exceptional career…

Pre-retirement form

Aided by the ‘date range’ feature on StatsBomb, we can analyse specific time periods in the league season, rather than his full campaign as a whole. This means we can effectively differentiate the periods before and after his emotional address, in order to see if there is a sizable improvement concerning his numbers.

Prior to his passionate announcement via a sit-down interview with his mental performance coach Jamie Edwards, Hart had attracted a considerable amount of criticism for displays leading up to this point. His sending-off versus Livingston – coupled with a poor display in De Kuip against Feyenoord – had many calling for a changing of the guard between Celtic’s sticks, with the experienced keeper struggling form under Brendan Rodgers.

Looking at Hart’s radar statistics up to February, there are areas in which the goalkeeper excels, and places where he has glaring weaknesses. Let’s start with the positives, as his ‘pass into danger’ percentage (a pass into a player that is being pressed or heavily marked) was only at 5 per cent, ranking him in the 100th percentile amongst his peers. Furthermore, his ‘positive outcome’ (How frequently the player is involved in sequences that are resolved with a positive outcome) was conveniently positive, in the 86th percentile with 1.85 per 90 minutes. 22.00 in aggressive distance was good going for the keeper, too, ranking him in the 93rd percentile in this metric.

However, Hart’s positioning in this period perhaps left a lot to be desired, making 1.81 errors per game concerning his placement in goals. Despite not being a terrible statistic – 43rd in percentile – the goalkeeper ranks around the halfway point in this metric. Elsewhere, his claiming percentage is zero, meaning a lowly 19th percentile for his efforts – or lack of – in this area.

Observing his shot map from the period of August to February above, you can see a lot of conceded goals in and around the six-yard box. Four are from longer range, including a sublime free-kick from range by Stephen Kingsley in Celtic’s 2-0 home defeat to Hearts back in December.

Post-retirement form

Since the announcement of his retirement from the professional game altogether, Hart’s performances seem to have stabilised, perhaps at peace with his decision to call it a day concerning his on-field career.

When looking at his StatsBomb data radar in this period, it is clear to see that improvements have been made in certain areas, such as shot stopping, claims and positioning errors, all which have seen positive statistical changes following Hart’s retirement announcement being made public. Although his pass into danger percentage has negatively risen slightly to seven per cent, it remains 93 in percentile, still a high return. Similarly, his positive outcome number has also lowered in value and percentile to 1.49 and 66 respectively, though the values as a whole paint a more balanced picture concerning his overall form in goals. Finally, his aggressive distance rose slightly to the 95th percentile, at 22.49 in overall value.

Although a smaller pool size due to a lesser amount of games in the timeframe, Hart’s shot map in this period makes for both good viewing and reading in general. He has only conceded one goal from range – a Blair Spittal screamer at Fir Park – and three from inside the six-yard box. Three of his ten goals conceded in the league have been penalties, whilst Cyriel Dessers’ header in the 2-1 Glasgow Derby at home was his most close-range concession. A definite upturn in form, for a player who was in the firing line prior to his career announcement.

Looking at the form book following Hart’s announcement, Celtic have won 12 games out of a total 14 in all competitions, with a 10-man loss to Hearts and that 3-3 draw to Rangers the only games the champions have failed to win. During this time, Hart has saved arguably his best form for when the team has needed him most, playing his part in a third league title in a row. What a way to finish your Celtic career, and in defiant fashion.

Summary

With such a seismic figure like Hart occupying the Celtic goal, the club have a difficult job on their hands with replacing the outgoing keeper. Admittedly, his best years are behind him, with 37 seeming like a good age to call it a day concerning his on-field career. You only have to look at the way Allan McGregor bowed out at Rangers to understand how important timing is, given his lowly end to an otherwise legendary career at the club.

Hart seems settled with his decision, and got the hero’s sendoff on Saturday versus St Mirren, where the Green Brigade’s 3D tifo moved the veteran goalkeeper to tears. He would repay the gesture by starting a chant following full-time with the Ultras group.

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The words of that specific chant are ‘Don’t worry, be happy’. Celtic, their manager and the hierarchy need to follow the song’s message and mantra by doing their utmost best to sufficiently replace Hart in the coming weeks and months. The sooner the better, especially with the club jetting off stateside in July for a pre-season tour. Ideally, his successor in between the sticks will have already been signed, sealed and delivered by then.

Either way, the heart that Hart has brought to the fold will be difficult – perhaps impossible - to replace in the transfer window this summer, as the search for his replacement commences.