Is Celtic's Set Play Defending Improving?

On last nights Huddle Breakdown (please subscribe to the channel!), we were asked by Pete Lacey (thank you), “Are (Celtic) getting better at defending set pieces?”.

A nice simple question!

Let’s look at some basics first.

Season Comparison

I can share data on this for the last five seasons on this for all competitions.

This shows the Expected Goals conceded from either Set Pieces or Corners, and the actual goals conceded from same, per 90m. Note that these are not all from the initial set play direct pass, and could be from a secondary phase following a set play pass.

This shows that the number of goals conceded by Celtic from set plays is increasing as a trend, but is slightly better than last year per 90m.

However, here is the trend line for xGA.

This is a much shallower incline over time.

And, again, xGA from set plays is improved over last season.

The second trend to highlight is that under Rodgers Celtic conceded fewer goals than expected from set plays. In 18/19 in particular, Celtic’s xGA suggested 11 conceded but only 6 were.

This could be luck or could be improved organisation having a bearing.

This trend reversed under Lennon and this season is the worst in terms of the differential between xGA (9.9) and actual gals conceded (16).

Bad luck, smaller defenders, lack of organisation / familiarity given the personnel changes?

This Season

It is very difficult to attribute luck. Also, it would need a thorough video analysis of all the set play scenarios to detect positional, communication and organisational root causes.

But in terms of the patterns the data gives us, here is the xGA over time as the season has unfolded.

That big spike on the far right by the way is Livingston away! A win, but with scars.

What I’d focus on is the Red line. This is the trendline showing how the average xGA from set plays per game is trending over time.

This shows that xGA given up from set plays is gradually but slowly decreasing over time.

Is that sufficient improvement? Well, Celtic are on track to concede more goals from set plays than in any of the last five seasons. 17/18 was the only season in the sample where goals conceded (0.13 per 90m) was broadly similar to xGA per 90m (0.18).

Conclusion

It seems as if as the season progresses, Celtic are giving up less chances from set plays. This is consistent with the general improvement in organisation witnessed.

What is also true is that Celtic’s overall performance in this regard has deteriorated over the last three seasons in terms of actual goals conceded. Some of this will be the vagaries of fortune. xGA has been fairly consistent at around 0.19 xGA per 90m.

The awful 20/21 season was hopefully the outlier but plenty of room for improvement.