By Dave Laidig (@davelaidig)

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.

And this is our goal here; to offer a performance measure for each player, compared to readily available “replacement players” in similar positions. Because soccer awards three points for wins and one for draws, I’ll use Points Above Replacement (PAR) instead of wins. In other words, we’ll estimate how much a player has contributed to his team’s overall standings – when compared to an easily-acquired, hypothetical bench player.

The elements of this statistic require a (1) performance measure based on game actions, (2) a reference group, and (3) a method for relating individual performance to team results.

Performance Measure

For first part, I use the performance measure described in previous articles (see, Player Value Recap (2018), where more details can be found). As reported earlier, the performance measure adds possession context to match events. And match events are then scored based on whether the actions increase or decrease the chances of scoring – based on how much similar actions, in the same areas of the pitch, affected historical possession results. Further, the performance measure has the benefit of reporting values in goal equivalents (GE).

Define “Replacement Player Level”

The second step is to define a reference group for the performance measure. Appropriating from baseball definitions for replacement players, I too decided the replacement players should represent a player that could easily be found at a minimum salary. In the US, and for MLS players, their salary information is publicly available (or at least a consistent proxy for what their salary may be). As a result, I define a “replacement player level” to be the average performance for players with a base salary of $67,000 or less.

In MLS, a $67,000 salary is the minimum salary for the supplemental roster. To be fair, Byzantine MLS roster rules mean a 67k player could be on the senior roster, or supplemental roster, or reserve roster. And some players making more could be placed on the supplemental roster via homegrown player or Generation Adidas exceptions, and perhaps many more reasons. Unsurprisingly, I did not want to get caught up interpreting MLS roster rules. Thus, MLS players (in the 2017 & 2018 seasons) with base salaries of $67,000 or lower are used to set the replacement player performance level.

One additional element is required for reference groups; the on-field position. Different roles lend themselves to different performance levels. And the most meaningful comparisons are like for like. As a result, I went through each match of the 2017 and 2018 seasons and identified the starting positions for players based on team formation. Substitutes are labeled “subs” – no attempt was made to assign a role to a substitute player (too labor intensive and subjective for subs).

The result led to twelve positional labels to cover forwards (LF, F, RF), midfielders (CAM, CM, LM, RM, DM), defenders (LB, RB, CB) and goalkeepers (GK). I used “CAM” for players lined up centrally between other midfielders and forwards; for example, the 1 in a 4-3-1-2. I used “DM” for central players lined up in the half space between defenders and other midfielders; such as the 2 in a 4-2-3-1.

Players were assigned to the position that they started in the most. If there was a tie, I used the position that best represented the roles the player assumed. For example, a hypothetical player with five starts at CM, five starts at LM, and three starts LB would be placed in the LM group – because he tied for starts between LM and CM, but most often plays on the left. If the role was still in doubt – or if their only experience was as a sub – then I placed in them in the central role of the first position group listed in the MLSPU salary spreadsheet (i.e., forwards are “F”, midfielders “CM” and defenders “CB”). This is not an exact science, but allows one to adjust if one has issues with my labels.

For practical purposes, I condensed the twelve positional labels into 6 replacement player reference groups. Attacking players consist of LF, RF, F, and CAM players. Wide midfielders are LM and RM players. The central midfielder category is made up of CM and DM midfielders. Fullbacks are the LB, and RB players. And the CB and GK categories consist of their namesakes respectively.