By Benedict Brady
Over the past few years, Isaiah Thomas has transformed from a role player into an obvious All-Star candidate. He is having a transcendent offensive year, and he has been particularly impressive in the 4th quarter. But in our analysis of the point guards, we came across something very interesting. Isaiah Thomas’s strong offensive season is being partially offset by his subpar defense. To be more specific, Thomas has a 9.1 offensive BPM, which ranks second among players who have played 15 or more games, and a -4.0 defensive BPM, which ranks dead last. This is a remarkable spread, but just how unusual is it?
To quantify this disparity, we can use BPM, a box score statistic that dates back into the 70s on basketball-reference. Looking at all the seasons since the ABA/NBA merger (1976-1977), we can rank all player seasons (minimum of 20 games played) by the absolute value of the difference between their offensive BPM (OBPM) and defensive BPM (DBPM). Here are the top 15:
As we can see, Isaiah Thomas in 2017 is second only to Darko Milicic under this metric. But, since OBPM and DBPM have different means and standard deviations, this may not be the best way to quantify this disparity. Alternatively, we can account for this by taking the z score of every player’s seasons (using every OBPM/DBPM season with more than 20 games as a reference distribution), and ranking seasons by absolute value of the difference between the offensive and defensive z scores. Here are the top 15 seasons under this new metric:
Now, Isaiah Thomas has moved to the top of the list, as his seasons are more of outliers relative to the mean. It is interesting to note that most of the players in a similar stratosphere under these two metrics are centers, who are solid defensively but are a massive negative offensively. In the final graphic here, we can see OBPM graphed versus DBPM:
Here we can see just how far Thomas is from every other player. There seems to be no comparable season with remotely similar attributes. While he is playing very well offensively, it seems unfair to not also mention his defensive struggles when evaluating his overall impact as a player.