Fan concepts of "dirty" and "clean" players often reflect perception bias. Fouls and cards mostly occur in place of defensive actions - either a duel crosses the line or the duel loser retaliates. The most frequent fouls come from the most frequent defenders. Attacking players are often more likely to commit a foul in a given duel, whether that's due to lesser defensive skill, referee bias, or the simple fact that the attacker is often not initiating the duel leading to a foul. Increasing share of a team's defensive actions accordingly leads to fewer fouls per defensive action:
To decide if one player is more prone to fouling than another, one must first compare him to others with similar defensive activity rates. The blue data points represent full-season performances for all MLS outfield players receiving over 1000 minutes of playing time for the past 2 years. No fancy calculations are needed to say new Seattle Sounders midfielder Michael Farfan - with his average performance of 2013 and 2015 shown by the red box - is a bit foul-prone.
|Player||Distance to Farfan||Player||Distance to Farfan|
|Oscar Boniek Garcia, 2015||0.136||Michael Bradley, 2015||0.229|
|Leonel Miranda, 2015||0.147||Cordell Cato, 2015||0.230|
|Oscar Boniek Garcia, 2014||0.166||Kelyn Rowe, 2015||0.232|
|Joevin Jones, 2015||0.169||Ambroise Oyongo, 2015||0.237|
|Ambroise Oyongo, 2014||0.179||Bernardo Anor, 2014||0.242|
|Igor Juliao, 2014||0.184||Benny Feilhaber, 2014||0.244|
|Brek Shea, 2015||0.187||Sal Zizzo, 2015||0.253|
|Rafael Ramos, 2015||0.195||Corey Ashe, 2014||0.256|
|Benny Feilhaber, 2015||0.206||Sanna Nyassi, 2015||0.258|
|Lee Nguyen, 2014||0.210||Collen Warner, 2014||0.261|
...but fancy calculations are what I do. The table shows the 20 closest performances to Farfan's previous MLS experience in terms of role distance among regular MLS outfield players, based on passing and defense shares, crossing, aerials, and dribbles rates, and pass length. Even when playing centrally, Farfan exhibited moderate crossing rates typical of creative midfielders and wingbacks. He also attempts to dribble around defenders at a rate characteristic of attacking players. Among Sounders, the closest role comparisons are Marco Pappa, v. 2015 (.286) and Cristian Roldan (0.302), not Andy Rose (0.565).
Farfan's creative numbers match up well up against the average of his 20 nearest neighbors, and he is a good long passer. He fouls too often, but is not exceptionally card-dangerous. His technical prowess and flexibility across the attacking midfield make him a solid, low-cost pickup for Seattle, but using him as a depth player likely reflects team commitment to other options backing up Osvaldo Alonso in defensive midfield roles (e.g. Roldan, Jordan Schweitzer, Brad Evans).
Raw data for this work was collected from OPTA via whoscored.com.