The Mid-term report series turns its beady attention to the centre back position. This part of the team has been a problem for Celtic for many years in terms of injury and lack of continuity. This season saw Ajer and Simunovic prepped to start the European qualifiers by being installed as first choice at the end of last season. This when the superior Benkovic was fit.
Despite best intentions, and characteristic of Celtic’s profile in this area, Ajer and Simunovic only appeared together for 90 minutes 5 times. £7m man Jullien came in permanently after the 3-4 Cluj disaster and following yet another Simunovic break down. He and Ajer have been partnered in every game since except for Partick Thistle and Hamilton Academical at home.
Indeed, the Ajer-Jullien axis is shaping up to be the first centre back pairing to both reach over 40 matches worth of minutes since Denayer and Van Dijk in 2014/15. Since then Boyata appeared in 39.25 worth of minutes in 2015/16 and Ajer 38.59 worth of minutes in 2018/19. Given Celtic are playing over 60 games a season and this is an area that works best with partnerships, that’s been a problem.
Defensive Performance
Focussing just on defensive actions, the following plots Defensive Action Success Rate % DASR%) and Possession Won from Defensive Actions %.
I have included all the centre backs from the Treble Years who have played more than 20 matches worth of minutes. I have also added Van Dijk and Denayer from 2014/15 as this was the last sustaining partnership over a season, and also, in my opinion, the most recent gold standard for centre back pairings.

Whilst it is still the case no one can get to Van Dijk’s DASR% of 84%, Ajer and Jullien are clearly operating at a higher level than any recent pairing. As can be seen above, 16/17 was a bit of a low point for centre back performances hence why Toure was brought in and Celtic conceded 50 goals the 54 under Rodgers.
17/18 saw the emergence of Ayer and the improvement of Boyata. Last season saw Boyata and Benkovic be the best performers despite Ajer and Simunovic ending the season as the selected pairing for expedient reasons.
But 19/20 Ajer, alongside new Bhoy Jullien are threatening to eclipse the performance of Denayer and Van Dijk as a pair, if not individually overtake the imperious Dutchman.
Why is this? Well, the continuity factor cannot be discounted. Celtic have had notorious bad luck with centre back injury but those two have now played nearly 30 matches together. There is a case the SPFL in particular is less competitive this season in terms of depth. Most clubs live within their means and therefore are at the mercy of player contracts. Clubs like Hearts and Hibernian have made bad managerial decisions and are therefore weaker. Aberdeen are declining after a successful cycle. Clarke left Kilmarnock. Also, there are no Champion’s League Group matches to potentially deflate performance. Neither was there is 2014/15 for Denayer and Van Dijk, interestingly enough. It may also be the case they are a lot more solid than vociferous critics believe.
Of the current centre backs Jullien is by far the more dominant defender with 2 more challenges/intercepts than Ajer per 90m and nearly 4 more than Bitton and Simunovic.
Defensive Error and Saves

I’ve documented many times that Bitton is error prone as a defender – he loses concentration and wanders out of position. Playing at the back can be a bonus against weaker opposition as his distribution is so good. It is astonishing to me however that he has deputised for Brown on so few occasions. Surely this is simply because of Simunovic’s injury and the need to have him as backup. This season, Simunovic also goes over my 0.5 threshold for acceptable numbers of defensive errors.
Nothing has divided my timeline on Twitter more than the decision to award Ajer Player of the Month for December on A Celtic State of Mind (ACSOM), a wonderful site I contribute modestly to. I can almost hear the gnashing of teeth from certain quarters as they see Ajer has the lowest error rate. Why so? Of the 11 errors I have tagged Ajer with, 5 have come in the last two meetings with The Rangers. Those higher profile performances were punctuated with uncertainty as well as being fresh in people’s minds. Some see errors against The Rangers as being more important than against anyone else – “Old Firm-itis” I call it. This in turn leads to selective memory where all the other performances are forgotten.
Bitton also has the most missed tackles (0.2 per 90m) whilst Simunovic has none. Simunovic and Jullien lead the way on possession lost in their own defensive 3rd. I find this is a result of those who effect more Clearances.
Defensive 3rd Wins and Recoveries
These two metrics speak to recovering the ball and especially within Celtic’s defensive 3rd.

Jullien leads the way by these metrics which speak to anticipation and positioning. Also, he is often one who engages first when the ball is launched forward by the opposition.
Ball Progression
Plotting total number of Open Play Passes and indicating how many of those are Pack Passes – forward passes that take out opponents.

Bitton is clearly the most prolific passer and over 9 of his passes per 90m take out opponents. As mentioned, it is a useful tactic when there is little defending to be done.
Jullien’s passing profile is otherwise the more interesting. He completes the fewest Open Play Passes (44 per 90m) yet the second highest Pack Passes with over 8. Whereas Simunovic complete 94% of his passes and the others are all over 90%, Jullien completes 89%. He puts more risk into his passing and that will be one of the features Lennon likes – he gets it forward that bit quicker and more often.
Ajer, of course, progresses the ball on the ground by dribbling. He completes an average of 6.06 ball carries per 90m (Pack Dribbles + Progressive Runs). Only Frimpong, Hayes, Morgan and Johnston complete more in the squad. Bitton is next on 3.91.
Conclusion
Ajer is the only remaining member of the 18/19 treble defence. As I have shown in the midterm reports for right and left back, the current incumbents are not yet an upgrade on Tierney and Lustig. Within this context, Ajer and Jullien have forged a partnership that has seen rare continuity, but more importantly, defensive performance fundamentals not seen since Denayer and Van Dijk. Some will scoff at that comparison but the numbers are clear and from over 30 appearances each so a good-sized sample.
Neither is perfect. Ajer has improved his manhandling of opponents but his left foot is as weak as ever, he goes to ground too often and jump timing can improve. Jullien tends to turn up for the big games a coast through the smaller ones – 10 of his 13 defensive errors have come against smaller SPFL sides. Jullien also tends to allow himself to get riled by unlikely opponents far too easily.
If they were better, they’d be at Barcelona. As Celtic centre backs, they are on course for a golden season. And no, the article does not claim either are individually on the same level as Van Dijk!