“Chances” are defined here as the sum of all assists, key passes, and shots. Offensive “touches” are the sum of basic passes, cross attempts, and shots. Evaluating player performance based on skill-dependent statistics is dependent upon a thorough assessment of player behavior. We need player typing to be as diverse as on-field roles, and as indifferent to nominal “position” as possible. The statistics used to characterize type should be characteristic of role and as far removed as possible from player quality/skill (e.g., shooting rate should discriminate attacking players, but the ability to generate shots is descriptive of quality, so it is not useful as a role-dependent statistic). Finally, we shouldn't use so many statistics in constructing a model of roles such that the result becomes overfit to specific players or contains redundancy (e.g. including two different types of basic passing rates – say, short passes and long passes – would exaggerate role difference specific to distribution).
For now, with the 2015 dataset, I assessed pass and defense share as described above.Goalkeepers have been excluded (it is interesting to include them in team analysis, but their position label is relatively effective). I also calculated and recorded dribbles/touch (measuring attacking style on the ball) and crosses per touch (wide vs. central play). I then relativized each of these four role indices to its 210-player maximum and performed a hierarchical cluster analysis on the resulting data matrix: