Saturday, July 12, 2014

You better run!

Most stats in this FIFA 2014 World Cup focus on shoots, attempts, saves, and fouls, while metrics associated with distance have been somewhat overlooked. While there may be a significant change in the kind of play between the former World Cup champions and the next ones in these terms (remember tiqui-taca?), let’s have a look at what happens to distances covered by the eight teams that reached the final stage of FIFA 2014.
Among all the parameters that can be calculated from match analysis, we chose a metric associated with the amount of “useful” distance covered by a team during a match, and we called it Run dominance:

As it can be seen from the equation, Run dominance is calculated as the fraction between two components:
- at the numerator, you average the distance covered by the team when in ball possession with the distance covered by the opposing team when the latter is defending. This summarizes the ability of each team to move when in possession, and to make the defending team move to oppose the attacks.
- at the denominator, you calculate the average distance covered in total by the two teams: it can be considered as an average measure of intensity in the match, to be used as a normalizing factor between low intensity ones (i.e. with low distances covered) and high intensity ones.
Thus, Run dominance can be seen as a measure of the amount of physical power associated with movement that a team displays during a match. The higher limit of 1 could be reached if the team were always in possession (and in that case, the opponent yields 0). Usually, distance covered in possession, distance covered in non-possession, and distance covered during dead times lie in the range 20-40% of the overall distance, which usually sums at around 200-250 km per match. With these figures, and under the hypothesis that the total distance was equally subdivided between the 3 situations, Run dominance would yield 0.33 for both teams. We collected data to obtain this parameter for the matches of the Round of 16 at FIFA 2014, and this is what we got for the teams that advanced to the round of 8:

By taking a look at the quarterfinal pairings, this metric seemed to predict that both Germany–France and Netherlands–Costarica would be lopsided, with the Teutons and the Dutch being the move-makers. Argentina might have proven similar against Belgium, while Colombia and Brazil were very close in these regards.
Make no mistake, though, dominance does not necessarily equal win in the football stadia (…but it might help ;)). Analysing extensively all the matches played up to now, it looks like Run Dominance is all but a bold predictor of the level of success of the national teams: despite Germany and Argentina ranking at the top of Run dominance, regression power stops at less than 0.1, which basically means that it does not predict scores, not even goals conceded.

However, Run dominance does predict fairly well the number of attempts that a team is able to produce in a game, as it can be seen from the figure below. And this predictor strongly correlates with possession percentage, with which it shares the regression power with the number of attempts per game.

By plotting Run dominance against possession percentage, teams above the line are those teams that are more prone to make the ball run more than the players when in possession, while teams below that line tend to move the ball when in possession. By looking at this latter graph, teams can be ranked according to the overall ability to be in control of the game. Most UEFA countries seem to lie above the regression line, almost regardless of the ability to direct a match, while CONMEBOL countries lie below that line (if we exclude Argentina, which have crossed the bar only after the final match). The other confederations do not a show a common behaviour, even if Australia and United States seem to behave in a similar manner to UEFA countries, as expected, given the presence of european managers.

Thus, with the representation of these two variables - possession percentage and Run dominance - one is able to collect two different measures: the amount of control in the match each team is able to produce (or concede to the other team) based on its position along the regression line, and the quality of this control (i.e., by making the players move when in possess, or making the ball move), captured by the relative distance from that line. This is even clearer in the figure below, where regression residuals are represented against possession percentage (CONMEBOL teams labelled in red, UEFA in green).

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