Data Rant: Van Gaal’s obsession with passing
Despite scoring the match winning goal at Villa Park, Adnan Januzaj was criticized by Louis Van Gaal for “unnecessary ball losses.” In fact, pass completion seems to be the chief criterion by which the Manchester United manager judges performance. Why does Van Gaal place such importance upon the passing and is pass completion a robust enough indicator of team performance? Data Rant investigates…
After all, possession, which is so inherently linked to pass completion, makes for a poor predictor of team performance. It has long been proven that tiki taka was a manifestation of Xavi Hernandez and Andres Iniesta’s preference, not vice versa – it was the Spaniards’ excellence that drove Barcelona to victory, rather than any superiority afforded by the approach.
Why then should pass completion warrant Van Gaal’s close attention? After all, the Dutch manager has taken the concept to such an extreme that even the centre-backs are chosen because they are “correct-footed.”
It is not all that difficult to artificially amp up the figure by playing safe passes. Indeed, one popular managerial approach is to set a particular number of passes that have to be made before the ball can progress further up the field. British managers, including David Moyes, swear by this.
The relationship between chances created, shots attempted and pass completion using data from all 40 Premier League games under Van Gaal has been charted, below, and there is little correlation. After all, lumping the ball to Maroune Fellaini can lead to attempts at goal, but is fundamentally inaccurate.
It is interesting, although expected, that the relationship between chances created and pass completion is almost double that between shots attempted and pass completion. The Van Gaal philosophy emphasizes picking the right moments. This may be interpreted as the oft-mentioned philosophy having some merit. This phenomenon is charted below.
Technical note: more sophisticated and powerful statistical indicators such as OLS have been omitted for the sake of brevity, but they suggest a nontrivial level of causality between defensive performance and pass completion.
The relationship between defence and pass completion, on the other hand, is strong. This point is worth fleshing out. The link between defence and possession has been long known – many technical sides defend by not letting the opposition have the ball. The link between defence and pass completion, though, escapes simple analysis.
A good pass completion rate does suggest a certain level of discipline and organisation. It could be that Van Gaal’s focus on passing has led to the Reds adopting a shape that is conducive, not only to keeping the ball moving accurately, but also defending well.
Another possible interpretation is that defenders play a significant role in keeping the passing flowing – perhaps this explains why Daley Blind is playing at centre-back. If this supposed causal link is indeed strong then having a good passer – or even Antonio Valencia, a highly accomplished, if unimaginative passer, at right-back – in the backline will improve defensive performance in general. There is a dearth of quality in United’s backline and the Dutch manager’s obsession with ball retention may very well be for defensive reasons.
The quality of top-flight football is such that no team, even the great sides such as Pep Guardiola’s Barcelona or Van Gaal’s Ajax, can completely dominate the opposition. In the era of counterattacking, dominance must be considered in proportion rather than in absolute numbers.
We define dominance ratio as: [chances created + shots attempted] / [chances conceded + shots conceded].
So the larger this number, the more dominant United was in that game. The relationship between dominance and pass completion, charted below, is fairly strong. The better the passing, the better the defence. A strong defence is, of course, a foundation for dominance. Given Van Gaal’s setup, ball retention and pass completion deserve much attention.
Indeed, this explains why there has been so little movement on United’s part to recruit a world-class central defender, even though one seems needed. The system, more specifically the philosophy, is such that passing ability is more important in maintaining overall defensive performance than defensive skill. The focus for remainder of the transfer window, therefore, is likely to be on the attack – especially with Wayne Rooney struggling.