Thursday, February 2, 2012

Interpreting the net passing statistic

I use a statistic that I refer to as "net passing" quite often in my analysis on this blog. Net passing is simply the number of passes completed by a team net of the number of passes completed by their opponent. The purpose of such a statistic is to provide a simple description of one aspect of the game: passing. Depending on a team's style of play and tactical approach, net passing may or may not be predictive of actual match outcomes. For example, some teams depend on possession and passing to break down an opposing team's defense. On the other hand, some teams play deeper and generate scoring opportunities on the counter attack. Playing on the counter attack requires much fewer passes, and consequently, net passing is probably not very predictive of performance for these teams. The figures below show the average points per game for each of the big six clubs by the level of net passing (as of game week 23).

(Click on figures to enlarge)

The light blue bars in the figures above indicate that the points per game statistic is based on only one or two games. As a result of such a small sample, these statistics are not very reliable. Manchester City have a high points per game irrespective of their net passing. Somewhat surprisingly, they have not dropped any points in games in which their opponents have out-passed them, and they have collected the fewest points per game from games in which they completed at least 301 more passes than opposing teams. Manchester United have collected on average only 1.33 points per game from those in which they were out-passed, while they have been markedly more effective in games in which they have a positive value for net passing. Remarkably, they have out-passed opponents by a margin greater than 200 passes on only two occasions. Tottenham also have a much higher points per game when they out-pass opponents, and the pattern appears more pronounced than that of Manchester United. Chelsea have averaged a respectable 1.6 points per game in games in which they were out-passed or completed 100 or fewer passes more than opposing teams. The incredibly low 0.25 points per game for the net passing category of 101-200 serves as an important reminder that statistics can yield strange results, especially when estimated from small sample sizes. Net passing seems to be quite predictive of Arsenal's performance, which is perhaps not surprising given Arsenal's style of play. Finally, there is little variation in points per game across net passing levels for Liverpool (ignoring the >300 category, which is based on only two games).

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