What are we trying to find by looking at on pitch statistics at an individual player level?
Shots vs. Goals
Their is a tendency for the coaches/media/fans to judge individuals on goals/assists for and against. The problem with using goals as a performance indicator is the fact that 'luck', or lack thereof, plays a massive part in scoring/conceding goals. Read these 2 links on PDO. Link1 Link2
It is my experience, from hockey analytics, that players and teams with a high PDO get a lot more 'praise' than players/teams with a low PDO.
High or low on pitch shooting %/Save% are not sustainable and will regress toward the average.
The more repeatable stat for determining performance is using total shots. Here is a great article on shot quantity vs. quality. If we can find out which players help increase shot differential, we can then increase the teams chance of scoring/saving a goal by playing them more or subbing them at the right times, therefore, leading to more points in the league table.
What I am looking for, are players who help increase total shot differential, of their team, while on the pitch. The higher the TSR% the more we know what part of the pitch the game was played in while a player is on the pitch. Raw on pitch TSR% is okay but does not provide context. What we see is that good teams have players with high TSR% and bad teams have players with lower TSR%.
The following stat allows us to differentiate players on the same team.
Relative Total Shot Number per 90 (TSR Rel/90) = Total Shot Number of player - Total Number of Team when player not on pitch
TSR Rel/90 begins to tell us who 'drives play' on his particular team. Helping create a shot for or stopping a shot against are equally important. Over the course of the season we will be able to see who has impacted shot ratios. Obviously, the higher the number the better.
What does a TSR Rel/90 of 1.25 mean? It is saying that for every 90 minutes that a player plays 11v11 versus every 90 minutes that he doesn't play, his team will be better off by a total shot differential of 1.25 per 90. The higher the number the better.
It is by no means a 'perfect' stat. As always, their are question marks. With 11 players on the pitch their is a lot of noise. The quality of the competition faced by each player, while he is on the pitch, is not accounted for. Game states or score effects are not taken into account. I just do not have the data and time integrate these into the analysis.
The general idea is to find a new way of analyzing players by removing goals from the equation. If we find a player who is very high or low we can look into his performances by watching film and looking at the quality of competition, quality of teammates, game states etc.