Central Winger: The true measure of passing efficiency has nothing to do with completion rate

Central Winger: Houston and Toronto passing

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In 2012, the Houston Dynamo and Toronto FC were on the opposite ends of the passing spectrum in MLS. But that doesn't tell the whole story, despite their equally opposite records last season.

By examining the passing trends of these two sides with the help of Opta's MLS Chalkboards, we can gain a better understanding of how their respective systems operated.

While Houston had one of the highest pass-completion rates in the league at around 80 percent, Toronto had the poorest – just south of 70 percent. But, as I will show, these pass-completion ratios may not be purely a representation of a team's overall passing skill.

As shown previously in this column, one of the major factors in pass completion is the distance of the pass. The longer a pass is, the more unlikely it is to have a successful outcome. By looking at the lengths of passes that Houston and Toronto attempted, we can gain significant understanding into why they had such disparate pass-completion ratios.

Above are pass-length distribution charts for both Houston and Toronto. The height of each column represents the number of passes attempted at the yard length specified below. The dark section of each column represents the number of those passes which were completed, while the remaining white area represents the number of passes that were incomplete.

By comparing the black-to-white ratio in each column, you get a glimpse into the pass-completion rates of specific pass lengths.

Central Winger: Possession trends and what they say about Major League Soccer

When compared, it's immediately clear why Houston outperformed Toronto in pass-completion rate by a significant margin. While the ratio of completed passes to attempted passes for certain pass lengths remain relatively constant between teams, the distribution of passing volume changes drastically. This difference is the major driving factor.

This is a tremendous illustration of why raw pass-completion percentages are poor performance indicators without controlling for some level of context. Houston and Toronto – and all other MLS teams – have only slightly statistically significant differences in passing completion ratios on passes that travel less than than 15 yards.

While Houston were undoubtedly a better passing team than Toronto, it was as much their pass selection as their passing skill that lead them to become one of the league leaders in pass completion rate.