I wrote back in May about the paradoxical nature of OPTA’s possession statistic in MLS—how more possession corresponds to better shot ratios, better shot ratios correspond to better goal differentials, but somehow more possession does not correspond to better goal differentials when we control for certain variables. In fact, I found that once I controlled for the teams playing in a given game, possession had a negative correlation with goal differential and winning.
The new data agrees with the old. Correlations suggest that team possession still correlates positively with scoring attempts (p-value = 0.01), scoring attempts still correlate positively to goal differential (p-value = 0.02), and now with more data, possession is also positively correlated to goal differential (p-value = 0.01). That all seems to line up with logic, but the paradox from before still exists.
When I look game-by-game and control for the home and away teams, in-game possession has a positive correlation to shot ratio, but a negative correlation to goal differential. In other words, the team that has more possession in a given game tends to also earn more shot attempts, but still loses more frequently than we would expect. As mentioned in the first article back in May, this seems paradoxical. I had some theories in that article, but reader David Stringer got me to think about another logical explanation.
Teams that develop leads tend to sit back more defensively, and often are satisfied allowing the opponent to possess all it wants in less dangerous parts of the pitch. A team that has a lead in the second half probably got that lead because it was generating more opportunities (read: attempts). It makes sense that the team that eventually went on to win also produced better shot ratios early on before getting the lead. After getting the lead, the team in front was willing to give up extreme possession relative to a more neutral shot rate. Thus it ends the game with poor possession, but a still favorable shot rate.
Just a theory, and I’d love to hear about other ideas! The stats are definitely not lying. These correlations are very real, but the causes for the possession paradox are still elusive.
American Soccer Analysis 
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I think the “possession paradox” is probably due to teams bunkering in after they get the lead. They have scored, and now they don’t need to possess the ball, they need to defend. Possession demands having players in advanced positions down the field, because teams aren’t going to want to hold the ball long in front of their own goal, especially not with the lead. Having players in advanced positions means more running for their players because they’re going to have to fall back to defense when their teams turns it over in order to protect the lead. Some teams don’t play this way but most do. Teams with the lead are generally going to pick and choose when they go forward, and then they’ll only go forward fairly cautiously keeping an extra man or two back on defense.
This paradox reminds me of something I noticed when I joined some friends’ fantasy football league for the first time a few years ago — a lot of time the losing quarterback in a game has better stats and puts up as many or more fantasy points as the winning quarterback. Why? Winning teams start handing the ball off to the running back to slow the game down and run out the clock while losing teams start airing it out to catch up. Lots of passes obviously will help a quarterback’s stats but that doesn’t mean they’re winning the game. Also, it can show a team that can move the ball but not put it in the end zone.
In soccer, I think it’s much the same. Not only is the winning team trying to kill the clock so they’re content with lots of turnovers as they kick it long up the field or out of bounds as long as minutes are taken off the clock but the “possession paradox” can also show a team that is frustrated in the offensive third as well. If the other team is not able to score, it’s easier to let that team keep the ball. If the other team is scoring, you don’t want to let them keep it!
I’m not sure I agree with Opta’s counting of touches instead of time in their possession stats, however. I think time of possession is more in line with how the game is played. A good team will control the game by slowing the game down at times and speeding it up at others. It would be interesting to see if the “possession paradox” exists for time of possession as well. Ideally, I would like to know both time of possession and the number of touches taken by a team. Not just passes, but dribbles as well.
It would also be interesting to break the rates of possession down by score as well — whether the teams are tied, one team up by a goal, two goals, etc. Then it would be easier to see how much a team’s rate of possession depends on the score and if teams were sacrificing possession in order to defend more effectively with the lead.
I also think it would be really interesting to look at possession (both time and touches/passes) by game state. In fact, that very well may explain the whole paradox that we’re seeing. If teams simply choose not to possess in advantageous game states, then the correlation makes a lot of sense.
In terms of fantasy football, I love it when my quarterback’s team goes down early. Rack those yards up!
Optas possessions statistics is based upon touches, if I’m not mistaken. But studies have been conducted by both and from my under standing neither specifically correlate to goals scored. However, chained passes–such as passes that are made in consecutive order Henry to Johnny Steele to Cahill back to Henry–if I understand it right has a higher correlative relationship to goals scored. I think there is a lot of chaos involved in possession that it may not ever be something that can be used in the sense that it’s representative of how a team specificly played. That said, I would love to do a Game state possession metric. It would be much more involved than what we (ASA) have the ability to conduct at this point. But maybe next season if we reach some of our goals we may be able go at it.