Celtic will be more efficient under Brendan Rodgers - James Dailey

What insight can we potentially acquire by comparing the 27 league games of that season under Rodgers to this past season under Ange Postecoglou? Overall performance levels, stylistic differences, potential positives and negatives - what else can we find?

The first radar was built to try and offer a broad summary of the two periods. From this summary it is clear that Postecoglou’s team had superior goal and xG differentials, whether including penalties or not. Both teams enjoyed similarly dominant possession levels, though Rodgers side was not as direct and attacked in a more deliberate fashion. Both sides played a relatively high defensive line, though Postecoglou’s was far more extreme, ranking in the 95th percentile versus 80th for Rodgers’. Lastly, the Northern Irishman's side enjoyed a significant advantage in OBV difference, at 1.36 versus 0.99 for Postecoglou.

This next radar focused on the nature of shots taken and conceded for both teams:

Here we see widespread similarities with a couple of notable exceptions. As reflected in the prior radar through his side playing an extreme high line, they were largely successful at snuffing out opponents’ ability to counter attack. Rodgers’ side were also relatively effective, but not to the same degree. His slide enjoyed edges in the number of clear shots taken, which is partly reflected in the superior shot OBV metric. A reminder: shot OBV includes the quality of finishing as well as the quality of decisions made relative to shooting versus other attacking options available to players. When I decompose those elements, it appears that Rodgers’ side were more effective finishers with comparable levels of decision-making.

READ MORE: Why Brendan Rodgers de-risks structural Celtic weakness

A standout metric in the radar is the degree to which Postecoglou’s side benefitted from extremely poor levels of play from opposition goalkeepers. In fact, that 0.56 disparity can be thought of as a per-game number of goals over the duration of games in question that opposing keepers boosted the level of goal scoring by Postecoglou’s side. Obviously, Celtic cannot control things like the quality of opposition keepers’ play but that element covers more than 100 per cent of the disparity in goal difference. If we adjust for the advantage in finishing quality from Rodgers’ side, the goal differences were nearly identical. 

The next radar compared a more comprehensive range of metrics related to defending and pressing, which offer additional context above and beyond the number of goals, shots, and xG conceded and the relative height of defensive lines: 

Here we see that despite the reputation of Ange-ball being an intense form of high press and counterpressing, it was Rodgers’ side that displayed higher volumes and greater efficiency for both. We see once again via the percentage of pressures and counterpressures in opposing half that Postecoglou’s side deployed their pressure higher up the pitch, on average. 

The last radar was comparing the various elements of OBV:

This radar touched on a similar theme to one explored in a recent column that attempted to quantify the contributions of Postecoglou versus the squad talent level by comparing with the 2019-2020 Celtic team. This OBV radar indicates a similar dynamic - that is there is some evidence that the talent level of the squad drove higher rates of OBV, while more systemic factors (playing style in particular) drove the overall disparity in performance levels. The gap persists even excluding the goalkeeper-related metric, as Scott Bain enjoyed an extremely ‘purple patch’ of shot-stopping over that particular period. 

Along with that prior column, a broader analytical mosaic with some nuanced positives and negatives emerges in the scenario of Rodgers replacing Postecoglou. A main positive is that from a strategic perspective, the evidence shows that Rodgers is at least an equal and perhaps better than Postecoglou relative to the ambition of Celtic competing better in Europe. Postecoglou’s style of play presented a double-edged sword of sorts - suffocating domestic competition but leaving the team very vulnerable defensively in Europe. 

READ MORE: The Celtic tactical tweaks Brendan Rodgers could implement

Rodgers’ reputation in Europe for his first tenure is unfairly harsh from a coaching and strategic perspective, in my opinion. His two Champions League campaigns did include heavy defeats, but those were to the likes of Barcelona and PSG, which included peak elite finishers in their primes, including names like Lionel Messi, Neymar and Edinson Cavani. Indeed, Postecoglou’s side surrendered large amounts of xG last season versus Real Madrid and RB Leipzig that could have easily resulted in hugely lopsided scorelines had those sides enjoyed similarly lethal finishing. 

Even within that first campaign, Rodgers’ side was competitive versus an emerging Manchester City behemoth and solid Borussia M’gladbach side after navigating the typically treacherous qualification path. In his second campaign, Celtic finished third behind PSG and Bayern Munich while conceding xG at a level well below that by Postecolgou’s side, despite facing what I would argue was a more difficult group. Losing a tight knockout tie versus Zenit, where Celtic continued a trend of non-Fraser Forster goalkeeper play that has been very poor in European competitions. 

A main potential negative is that my assessment of the current squad is well below what appears to be the consensus amongst the fanbase. Relative to Rodgers’ preference for size, pace and power in his players, those are athletic profiles that are lacking in the squad in which he inherits. Fortunately, there appear to be considerable resources that will be available to better align and upgrade the squad.