Football is, in many senses, a very simple game to play. However, to truly play it well can be very difficult indeed. The great sides of world football come in all shapes, sizes and approaches, but they all possess an unerring ability to produce results when others cannot.
The good thing about recent developments in football analysis is that statistical information about sides' performances are readily available.
Now, besides commenting on the general playing style of a side, analysts are able to deconstruct and pinpoint which areas of the game are able to give the best sides their upper hand.
There are, of course, intangible attributes such as the familiarity and mental fortitude of a side. However, these tend to manifest themselves in tangible statistics.
Barcelona's familiarity as a team, for example, is part of the reason why their possession statistics may be higher than usual or why they are able to play more through balls per game than most other sides.
But, is there statistical common ground between the European elite in spite of their differing playing styles?
It goes without saying that good sides would expect to consistently perform well in terms of possession, defensive solidity and opportunities created, but which of these is more important?
The Possession Argument
The likes of Barcelona, Bayern Munich, Manchester United and Chelsea, for example, all register comfortably above 50 percent of possession in their Champions League runs this season. Likewise, the same sides all score highly in terms of pass completion. However, their performances have produced very different overall outcomes in this year's tournament (Whoscored).
Juventus and Borussia Dortmund, meanwhile, score poorly compared to their rivals on both fronts. They will, though, both point to the fact that they faced some of Europe's more adept ball-playing sides throughout their respective Champions League runs.
Possession, when used well, is a valuable asset. But, is there then an argument that efficiency when on the ball is a much more important and overlooked side of the game?
Attacking and Defensive Strength
Rather than look at shots per game, lets take a look at shots on target per game. A shot on goal could be struck from anywhere and—while some hopeful efforts may be on target—it is the second statistic that should give a better indication of which sides create the most meaningful opportunities per game.
Surprisingly, in this respect, Chelsea lead the way. However, the four eventual semifinalists in this year's competition can all be found among the top six sides in terms of shots on target per game.
Also among those edging to the top of the pile are Paris Saint-Germain and Manchester United—both of whom will feel very unlucky to have exited the competition in the manner they did.
Perhaps, then, it is the ability to create chances on goal, rather than retain possession, that is most important to a side's chances of success.
While “Shots on target against” statistics are not readily available, it is important to find some way of evaluating the importance of defence. So, using a general “shots conceded per game” statistic, we can see that the likes of Bayern Munich, Barcelona and Borussia Dortmund once again score well.
Some of those who disappointed, Manchester City and Chelsea for example, score particularly poorly in this respect.
We need, though, to find a way of discovering which teams find the best balance between these attacking and defensive statistics.
Striking a Balance—The Equation
If we can find the ratio of a team's shots on target per game compared to their shots conceded, we can establish a good idea of a team's chances of outscoring their opponent.
By combining this ratio with possession, albeit via a very crude equation, we should be able to obtain a fair understanding of the control they exert on a game.
As shown then, our four semifinalists all rank among the top five sides under this equation. It must be added that the four are all perceived to be in the semifinal on merit and represent most people's vision of the best four sides in Europe.
Looking at Anomalies
Porto (as highlighted) perform particularly well, given their Last 16 exit to Malaga. However, it should be factored into the equation that, by virtue of early elimination, they avoided meeting one of Europe's higher-rated sides.
A group including both Dynamo Kiev and Dinamo Zagreb, neither of which managed a win against the group's two stronger teams, can be seen as aiding their performance in this respect. The Croatians, for example, scored just one goal in the tournament
Likewise, both Manchester City and Juventus will point to the difficulty of their Champions League journeys to explain their performances. However, it must be remembered that Juventus also benefited from meetings with both FC Nordsjaelland and Celtic.
For Juventus, the problem in Europe has been creating chances. They have hit the target considerably less per match (5.3) than all the major title contenders, and it appears to have been this that hindered their chances.
Indeed, upon exit to Bayern Munich, the Italian champions rarely threatened to find an opening. Statistics would appear to suggest that this issue has been more than just a one-off occurrence.
For the English clubs, the number of shots conceded per game will be an equally worrying statistic, with all three sides examined allowing opponents more than 15 shots per game.
Taking the Champions League as our reference point, it appears that the key to becoming a top side is balance. A team must find fluidity and creativity in attack whilst also securing themselves defensively. It is in this respect that the English clubs have struggled this campaign.
Possession clearly helps, as it should enable the balance to be swung in a side's direction. However, it is far from the crux of the debate.
Ideally, a better formula to discover a team's degree of control on a game would be calculated. For now, though, the statistics we have in front of us give a good understanding of just why the continent's leading teams are quite so successful.
Ultimately, it appears that those who have progressed to the latter stages are those sides who come closest to finding the perfect harmony between attacking strength, ball retention and defensive solidity.
It is a logical conclusion, one that could be further developed with analysis of the aspects within these general headings that make them so strong.
Is it, for instance, that they are quicker to pressure opponents? Are they more selective with when to throw players forward? Or is it just that they have players more adept in their roles? It would be interesting to discover.