The Plexiglas Principle

Imagine, if you will, a world of legwarmers, neon spandex, and hi-top fades. The year is 1983, and New Order’s ‘Blue Monday’ is the must-have soundtrack for your summer.

As a discerning fantasy stathead, however, you have time to savour only one thing: the annual release of Bill James’ Baseball Abstract.

PLEXIGLAS PRINCIPLE EXPLAINED

To overstate the impact of James’ work upon the sabermetric community is a difficult task. Beginning in 1977, his annual compilation of statistics from the previous year of baseball laid the foundation for generations of sports analytics publications to come (this in spite of the first iteration of this booklet selling only seventy-five copies). It was the 1983 edition, though, that introduced the subject of this article: the expectation of regression to the mean, which he dubbed ‘The Plexiglas principle’.

At its heart, the Plexiglas principle simply states that players or teams which exceed expectations one year should not be inherently expected to continue to perform at such a level come the next. Nor should teams which fail to meet their expectations be considered as more likely for failure the next year.

Instead, James argues, we should expect outliers on either end of our distribution of results to regress towards the group average.

COLUMBUS CREW AS AN EXAMPLE

Columbus Crew had a poor chance conversion rate in 2019. While an average Major League Soccer side converts roughly 10.7% of its chances into goals, Columbus did so at a league-worst rate of 7.5%. Over the course of a season, this cost the Crew a deficit of 10.1 goals relative to the average team.

However, the rate at which a team converts its chances was shown to be essentially random from one season to the next. A comparison of 20117 and 2018 data for all Major League Soccer teams shows these two numbers to be totally uncorrelated to one another (R2=0.0022).

Indeed, the previous season, Columbus actually registered the fifth-best chance conversion rate in the league.

Over performers and under performers in this category should naturally be expected to regress towards average performance the following year: a prime example of the Plexiglas principle outlined by James.

With this in mind, here are three more teams who under performed their expected chance conversion rate in 2018. Those who struggled may offer great potential to the Fantasy manager going into the new season– particularly if last season’s performance leads to drop in price.

THREE POTENTIAL IMPROVING SIDES FOR 2017/18

Colorado Rapids

After Columbus Crew, the side who struggled the most to convert chances were Colorado Rapids. As anybody who held onto Dominique Badji through March and April can confirm, Rapid’s attackers seemed almost allergic to the act of scoring. Throughout a disappointing season, though, their chance creation numbers remained impressive. In fact, across the entire season, Rapids created a similar number of chances (208 vs 211) to their crosstown neighbours Real Salt Lake – and only Real the woodwork more times than Rapid’s 13. The key difference between these two sides was the ability to finish these chances: from the same number of opportunities, Real created a whopping 80 goals; Rapid's produced only 54.

A rebound is almost certainly due. The previous season, Rapid's tied for fifth in chance conversion rate (one spot below LA Galaxy) – and had finished above average in finishing rate every season back to 2011 (the first year for which I have data). A revival in Rapid’s attacking fortunes is expected, and should bring with it great Fantasy potential – lifting the already high sophomore-year expectations of players such as Jack Price and Kellyn Acosta.

Montreal Impact

Another side whose offensive numbers slumped drastically in 2019 were Monteal Impact. The Impact finished as the third-best offensive side in 2018, only to fall to the third-worst last season. Impact fans might feel inclined to blame this slump upon the loss of Daniel Kimunbe; yet others clearly deserve to shoulder some of this blame. Saphir Taider, in particular, saw his offensive numbers slide last season: despite making two additional starts compared to the 2017 season, Taider produced fewer goals, shots, touches in the box, assists, and chances created.

Come next season, however, fans of Montreal Impact should have hope for an improvement in their side’s attacking fortunes. In particular, much is expected of Argentine playmaker Ignacio Piatti who, having assumed the primary playmaking role for the Impact, looks set to build on an intriguing past campaign which saw him register 145 Fantasy  points – top among the Montreal squad.

Chicago Fire

The Chicago Fire are perhaps the most speculative of the three sides listed here, but their 2019 woes in front of goal are nonetheless due to improve heading into next year’s campaign.

Unlike the other sides listed here, the underlying numbers offer little in terms of optimism: Chicago Fire finished 17th overall in terms of goals scored and big chances created, and 8th in the Eastern Conference.

Nemanja Nikolic, who produced double-digit goals for the second year in succession, was the lone bright spot in the Chicago attacking line – and even he slumped terribly towards the end of the season, without a single goal or assist over the final eight games of the season.

Yet all is not lost for the Fire. Investment in attack is certainly required – with Nemanja Nikolic now on the free agent list and Nicolas Gaitan not making such a big impact as expected, attacking options are scarce. However, the arrival of reinforcements – coupled with the return of creative maestro Aleksander Katai from a serious knee injury – could signal an improvement for Chicago Fire in 2020….alternatively, they can always rely on CJ Sapong to inexplicably score twice every game.