Ange Postecoglou's Celtic reign was trending down

This is consistent with Ange Postecoglou’s playing style elsewhere, as Celtic conceded 53 goals across all competitions in 53 matches.

It was always about attacking intensity and the belief that you would score more goals than the opposition.

It is to the Australian's credit that he was good to his word in building a thrilling, attacking brand of football in a relatively short amount of time.

Indeed, between 20th September 2021 (following the defeat at Livingston) and 12th May 2023 (599 days!), his Celtic side lost one meaningful league game. That was to St Mirren, where six personnel changes were made, and the defence included Anthony Ralston, Stephen Welsh and Moritz Jenz behind a midfield of Aaron Mooy and David Turnbull. In short, a long way from a “first choice” starting XI.

Up to the point the title was won at Tynecastle on May 7, Celtic were on course for well over 100 league points. As I have written here, the slight “slump” in form post title confirmation is entirely in keeping with similar circumstances in the 21st century.

So, as we face into the age beyond Postecoglou, reflecting, was he good to his word on team style and was more success inevitable had he stayed longer?

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Data is unforgiving of course and heeds no calls from the English Premier League nor worries too much about signing on bonuses and pension plans. Nor does it have an agent! *Shakes fist at Frank Trimboli.

In that regard, it is a loyal servant but will, equally, not tell you what you want to hear, but stoically reveal only that as it is.

Before I descend into emotional wistfulness, rolling six-match expected goals differentials is the bromide we all need in our tea!

xG For and Against

The below chart plots expected goals for and against calculated as a rolling six-match average over the reign of Postecoglou. Trend lines are also included.

After an erratic start as the shock of “Angeball” immersion penetrated the Celtic nervous system, things steadied as the 2021/22 season played out to ultimately comfortable success.

The 2022/23 season started with no qualification rounds for Europe, one game a week and a free and long summer in which to work on attacking patterns.

The result was a tremendous start that laid the foundations for the campaign. However, it was a difficult high watermark to maintain and when Champions League football occupied the midweeks, a dip was inevitable.

Towards the end of the year, with Europe a distant and chastising memory, things picked up again but not to the same extent as the relentless start to the season.

It would be wrong to position it that Celtic limped over the finish line this term, but the side never recaptured the intensity and consistency of performances that characterised those autumnal weekends.

Both expected goals for and against began trending in the wrong direction. We must acknowledge the post-title win anomaly whereby the mountain had been scaled and players were mentally focussing on Cup Final success as a priority.

What is undeniable, however, is that over a two-year period, the trend lines are pointing the wrong way as regards improvement.

Here is the expected goals difference summary:

What should be emphasized is that a consistent xG differential of between 1.5 and 2 is going to lead to many victories over the long term. If you are around two goals (expected) better than the opponent every game, you need a lot of luck and general positive variance to make that up.

So, the underlying performances at the domestic level remain hugely positive, but the trend is declining.

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You must account for post-title drop-off. And there is an undeniable tendency to reduce the difference in between demanding European ties. Also, who is to say with recruitment, a squad refresh and another summer of coaching, that the 2023/24 season would not have been bigger and better?

Similarly, how long can you continue to drive the same players relentlessly forward? How many times can you repeat the same messages and motivations? Is decline and the need to reset and refresh inevitable under a style so physically (and mentally) demanding as “Angeball”?

We will never know, of course, but the opportunity is there now for a new manager to strive to match and then exceed what was a very high benchmark.