Fellow Hot Time in Old Town writer Adam Merges posted an article questioning whether the 2016 Chicago Fire defense is actually improved compared to recent seasons. Merges starts by exploring how soccer teams have to look at defense and how it compares to some other major sports. It does differ in some respects to sports where this adage is apt. In American football, for example, if the offense has the ball and controls the clock, it is highly unlikely the opposition can score. It is different in sports with flowing play where teams have to play either offense or defense at a moment’s notice.
Merges then moves on to some of the poor shooting statistics of the Chicago Fire’s offense (20 shots on goal through 9 games) and the defense (giving up 60 shots on goal in 9 games). These are scary stats through about a quarter of the season, but I took some exception to his assertions regarding the remainder of the season. Merges flatly states that if they continue to play this way, the opponents will eventually start scoring at a higher rate. This may happen, but it seems to be just as likely that they continue to play as they are and that they keep the goal scoring rate of the opponent as low as it has been. This rate is dependent on shot quality and if teams don’t get good looks (something totally in the defenders’ control), they likely won’t start scoring more. Now, they very well could regress to the mean and start letting goals at a higher rate but I see no reason to think this is inevitable.
I took to the comments section of Merges’ article to provide a more optimistic view:
The best defense is a good offense is what they say. Your point about getting a lot of chances is valid, but isn’t it good that they are limiting goals and just giving up chances? One has to assume that when (or if?) the offense picks up, the chances for the opposition will be reduced. If they are able to maintain a similar percentage of goals conceded per chance, shouldn’t that bode well for their goals against? I know it is never that simple, but I still see it as a sign of optimism.
I decided to investigate a bit further using some statistical analysis. It seemed logical to me that a team that faces a lot of shots per game (like the 2016 Chicago Fire) would have less opportunity to get shots on goal of their opponent (also like the 2016 team). If this is true, the opposite would probably be true (meaning spending more time shooting on the opponent decreases the shots the team’s own keeper would face). Play cannot be at both ends of the field at the same time, right?
Finding a Relationship in the Data
I used data from www.mlssoccer.com to compile season stats for each team from 2007-2016 to see how shots on goal compared to shots faced by the team’s keeper. Since some seasons had fewer games than other and since the 2016 is not complete, I converted these figures to shots per game. This gave me a sample size of 165 team seasons to see how these data points compared and see if there was a strong relationship one way or another. I calculated the R Value of the data and it was 0.0352 (on a scale of -1 to 1). I was shocked that there was close to no correlation between shots on goal and shots faced. Defensive assumptions cannot be drawn by the success of the team’s offense and visa versa.
The data is scattered with a mean 4.659 shots on goal per game and an average of 4.624 shots faced per game.
It is possible that the offensive and defensive statistics I chose do not represent the offensive and defensive prowess of a soccer team, in which case this analysis neither proves nor disproves the assertions I have made.
It is also reasonable to think that the play in MLS is more direct and that games can be played end to end, in which case both teams could have similar shots on goal and shots faced stats. I suspect if one were to analyze Barcelona using these two statistics, it would look much different. They advance down the field very methodically and don’t give opponents much time to shoot on goal.
No matter what this exercise says about offense and defense on a soccer field, I can definitively say that there is no correlation between a team’s shots on goal and shots the team’s keeper faces.
Further Notes on 2016 Chicago Fire
It is hard draw too many statistical conclusions on the Chicago Fire’s shot numbers this season because they have only played 9 games, but they are off to a historically bad start. Their 6.667 shots on target faced per game is only better than one team in the last 9-1/4 seasons of MLS. The only worse team was the 2007 Real Salt Lake team that faced 6.833 shots per game. They ended up second from the bottom in the Supporters’ Shield standings on 27 points (from 30 games) and gave up 45 goals that season.
The Fire’s 2.222 shots on goal per game would be the worst offensive performance of the last decade if their form holds through the summer and fall. The next worse is the 2013 Toronto FC team that only had 3.176 shots on goal per game. They finished 17th of 19 teams in the league that year and earned 29 points (from 34 games). They only scored 30 goals in the 2013 season.
Not good...not good at all...