We've looked at metrics quantifying the clutchness of individual NBA players before, but what about from a team perspective? Is there a way to analyze the quality of a general manager, in making decisions about team selection and player acquisition?
This week, we aim to aquantify team chemistry - how well the players work together as opposed to individually. Then, we map out team chemistry in relation to player retention to see whether GMs can identify when they have good core teams or when they need to mix it up.
To quantify team chemistry, we compared the expected win share of each team (totaled individual win shares of each player on the roster) with the realized win share. We had to calculate expected win share per player as a point of comparison, because actual win shares are already impacted by team chemistry - players will score more points if they are on a team that works well together. Expected win-share would give us a baseline for how players perform on a neutral team.
To calculate expected win share, we used a metric called a similarity score, which quantifies how similar two players' career trajectories are. We used 2013-14 data to calculate these similarity scores, and predicted each player's win-share by the win-shares of the 20 most similar players at this point in their career trajectory, weighted by their similarity score. By using these other players, we hoped to average out the team effect and isolate the individual effect.
By totaling up these expected win-shares and realized win shares for everyone on a team's roster, we could quantify the "chemistry", or the performance above individual expectation, a team had. Then, we plotted this chemistry metric against retention. Retention was also measured based on win share - we calculated the win-share total of a team in one year, then the percent of the win-share that would remain next year after some players were traded away.
On the other side of the spectrum, low retention and below-average performance teams are usually in the rebuilding stage, and GMs should continue looking for a better roster. High retention and below-average performance franchises are signs of teams falling apart in their chemistry, and GMs should seriously consider making some key changes to their roster.
The Lakers Are Doing It Right
The Knicks Are Not Doing it Right
|Retention vs. Performance Above Expectation for the New York Knicks|
Is Lebron Right about the 76ers?
Indeed, it seems that the 76ers are quantifiably in a "transition" process, as Lebron called it. Looking at the past three years, they've had performance below expectation, but also low retention rates, indicating that their GM is aware of the fact that he has to shuffle his roster up. This marks a strategy turnaround from years 2007-10, when they appeared to retain heavily in spite of their dismal performance.
What This Means for the 2015-2016 Season
|Retention vs. Performance Above Expectation for 2014-2015 Season Teams|
Some may argue that acquisition decisions are largely due to luck, and it is very difficult to attribute player performances to the competence of general managers. While this is a valid point, we hope that this data will cast some insight not on whether teams got lucky with the decisions they made, but rather whether they took advantage of favorable situations, such as converting high potential teams (top left) into a high-quality cohesive group (top right).