Plus-minus measures the impact of a player on their team’s performance. Originally invented by hockey general managers, every player on the ice is awarded a plus when their team scores a goal while every opponent player on ice gets a minus. The higher the plus-minus rating, higher the net positive of goals scored for a player’s team. In terms of plus-minus, the beste player has the highest plus-minus score, and the worst player has the lowest. Plus-minus has also been modified for use in basketball, first by 82games, and now more famously by ESPNRead More
Points Above Replacement
I recently created a decent set of MLS possession data while working on another project, and I was curious if the patterns of the famous Reep analysis would hold for MLS. Thus, I attempted to replicate his result, and perhaps offer a couple new perspectives to the data.
I was first introduced to the legacy of Charles Reep while reading The Numbers Game (by Chris Anderson & David Sally). Reep was an early advocate for applying statistics to soccer, and was famous for tracking game events by hand over many seasons. According to his data, most goals were scored from possessions with three passes or fewer. And this was taken as empirical justification to play directly; minimizing the touches with longer passes in order to improve results.
Although Reep’s status as a pioneer in the sport is secure, many still debate the results and interpretation. Some critiques assert the underlying data was misinterpreted. Highlighting a simple majority of goals may not be the best analysis when most possessions had three or fewer passes anyway. Others suggest the structure of the analysis confuses correlation with causation; leading to misapplication of the results. In short, one can’t tell if the results were caused by the number of passes, or whether some other factors have causal roles. As I attempt to recreate the analysis; it’s worth stating the same criticisms and critiques apply to this replication effort as well.Read More
Baseball popularized the use of the Wins Above Replacement (WAR) statistic; representing a player’s estimated contribution to a team’s win tally above what a generic replacement would contribute. In this sense, it’s a roster management tool to support a keep/replace decision. However, WAR stats are often used by others for general performance comparisons. But soccer (or football if you like) does not have widespread use of a WAR-like statistic.
In soccer, performance indices are typically confidential and proprietary, making it difficult to verify their validity. Teams and analysts, understandably so, do not want to give away their competitive advantage. And those that are shared publicly, do not usually describe values in terms of team performance, or comparisons to replacements.Read More