Central Winger: Why possession stats are misleading

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Possession is a statistic that is notoriously misleading. As suggested in last week's article, it has been found in MLS (and leagues abroad) that winning a game's possession battle can have little influence on actually winning that particular game. In light of some of these findings, this week's article focuses on ways to improve our understanding of this statistic.

Soccer games are supposed to be 90 minutes long. That's when the final whistle blows.

Depending upon how a particular game is being played, though, the amount of time that the ball is "active" can vary tremendously. For example, imagine two games – one relatively free-flowing game that has 80 minutes of active play, and the other a game plagued with ticky-tack fouls and anti-soccer tactics that sees the ball in play for just 60 minutes. These are not numbers pulled from a hat – many media outlets reported an average around 70 minutes of actual play during the 2010 World Cup.

Italians call it "The Right of the Weak" to destroy games against a superior opponent, and here's why: In these two extreme scenarios, teams that split possession 60-40 have incredibly different amounts of time on the ball. In the 80-minute game, possession is split 48 minutes to 32 minutes. In the 60-minute game, possession is split 36 minutes to 24 minutes.

Think a team like Barcelona would like an extra 12 minutes on the ball every game? At the very least, that's what they'll get if you don't slow the game down against them.

Another way to look at it: If Barça split posession 50-50 in a 70-minute game, they get 35 minutes on the ball. If they put in a dominant 60-40 performance in a 60-minute game, they get exactly one more minute of time controlling play.

   Team Possessions Goals Poss/Game Poss/Goal
1 New York Red Bulls  6,624  50 194.8 132.5
2 Seattle Sounders FC  7,434  56 218.6 132.8
3  Sporting Kansas City     6,781  50 199.4 135.6
4  D.C. United              6,672  49 196.2 136.2
5  LA Galaxy       6,766  48 199.0 141.0
6  Chicago Fire             6,642  46 195.4 144.4
7  Colorado Rapids          6,455  44 189.9 146.7
8  Houston Dynamo           6,909  45 203.2 153.5
9  Philadelphia Union       6,873  44 202.1 156.2
10  Real Salt Lake           6,920  44 203.5 157.3
11  FC Dallas                6,620  42 194.7 157.6
12  Columbus Crew            6,798  43 199.9 158.1
13  Portland Timbers         6,531  40 192.1 163.3
14  Chivas USA               6,713  41 197.4 163.7
15  New England Revolution   6,307  38 185.5 166.0
16  San Jose Earthquakes     6,911  40 203.3 172.8
17  Toronto FC               6,457  36 189.9 179.4
18  Vancouver Whitecaps      6,681  35 196.5 190.9

As you see in the table above, with info gleaned from the Opta Chalkboards, we'll then have to discuss possession a different way – by counting the amount of times a particular team possesses the ball.

When defining "possession" as a sequence of events by one team that included at least one attempted pass, the Sounders led the league with 7,434 (or 218.6 per game). Conversely, the New England Revolution landed on the bottom of the chart with 6,307 possessions (or 185.5 per game).

By adding goals scored, we can get a feel for the amount of possessions that it tends to take a particular team to score a goal. According to these statistics, New York Red Bulls were the most efficient, scoring a goal every 132.5 possessions on average. Vancouver, on the other hand, had the lowest possession efficiency, scoring at the rate of one goal every 190.9 possessions.

However, possession is not exclusively an offensive statistic. When winning, teams often use lengthy possessions to try and close out the game. The less possessions left, after all, the less likely your opponent is to score.

Thus, we have two different modes of possession: "attack-minded," when a team is actively searching for a goal, and "clock-killing," where a team is looking to grind an opponent down and protect a lead.

Leaving only "attack-minded" possessions, then, we can extract much more accurate offensive efficiency statistics.

   Team Possessions Goals Poss/Goal
1  New York Red Bulls       4,885   37  132.0
2  Colorado Rapids          4,851   35  138.6
3  LA Galaxy       4,622   33  140.1
4  Seattle Sounders FC      5,346   38  140.7
5  New England Revolution   4,763   32  148.8
6  Chicago Fire             5,406   36  150.2
7  FC Dallas                5,095   33  154.4
8  Philadelphia Union       5,371   34  158.0
9  Sporting Kansas City     4,919   31  158.7
10  Chivas USA               5,398   34  158.8
11  Houston Dynamo           5,463   34  160.7
12  D.C. United              5,204   32  162.6
13  Columbus Crew            5,803   35  165.8
14  Portland Timbers         4,619   27  171.1
15  Real Salt Lake           4,846   28  173.1
16  San Jose Earthquakes     5,363   30  178.8
17  Toronto FC               5,471   29  188.7
18  Vancouver Whitecaps      5,502   28  196.5

While these results are not stunningly different, there are some very interesting changes. For example, the New England Revolution jumped from 15th to 5th. I suppose this makes sense, as the Revs' main problem last year was defense. Their goals-against total was 32 percent higher than the league average while their goals-for total was only 16 percent lower.

Clearly, by digging into possession deeper than simple percentiles, we can begin to better understand this deeply flawed statistic.

Devin Pleuler is a computer science graduate from Wentworth Institute of Technology in Boston, where he played on the men's varsity team as a goalkeeper. He's certified as a coach through both the USSF and NSCAA, and writes the Central Winger analytics column for MLSsoccer.com.