Is the Celtic’s 3-Point Percentage Defense for Real? A Statistical Perspective

In a recent Dunc’d On podcast (which I highly recommend as a great listen for NBA fans), the hosts Danny and Nate briefly commented upon how the Celtics defense this season has been bolstered by the league’s second best 3-point defense, in terms of percentage of opponent makes. They also mentioned, however, that many NBA thinkers speculate 3-point percentage defense may be mostly due to luck and beyond the defense’s control. In fact, many argue that the best indicator of a good 3-point defense is the ability to limit opponent 3-point attempts, particularly the dangerous corner threes. I have previously written a little about 3-point defense for

With the conventional wisdom in mind, it also should be noted that the Celtics under coach Brad Stevens have consistently performed well in 3-point percentage defense. Boston has been a top five ranked team in this regard during each of the five years (if we include the current season) of the Stevens tenure. Perhaps there is something more than luck going on here? I decided to investigate this more deeply.

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Explanation of Threes and Layups NBA Net Rating Calculator


Today I released the Threes and Layups NBA Net Rating Calculator, an interactive web application that is an updated version of what I called the Threes and Layups Season Simulator before. To go to the app,  click the link above or click on the the link on the right side of the page under “Interactive Web Applications”.  Throughout the season, the application will be updated with up-to-date statistics.

First, a bit of background.

An NBA team’s Net Rating is simply the number of points per 100 possessions that they score (called Offensive Rating) minus the number of points per possessions that their opponents score (called Defensive Rating). A team’s Net Rating is essentially a one number summary of how well they have played.

The Threes and Layups NBA Net Rating Calculator allows you to see just how much better or worse a team would play if they improved or regressed in one of what I call the “fundamental” statistics. These statistics capture how well a team is doing in Dean Oliver’s “Four Factors”: shooting from the field, foul shooting, rebounding, and turnovers.

How to Use the App:

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How many possessions does an NBA lineup need to play before we are confident it is good?

Plus-minus data is at the bedrock of a lot of thoughtful NBA analysis. If I tell you that the Celtics have outscored their opponents by 153 points in the 350 minutes that Jaylen Brown, Marcus Smart, and Al Horford have shared the court this season (per basketball reference), then you might reasonably conclude that these players are doing something right when they are playing together. At the end of the day, a valuable lineup needs to have a good raw plus-minus score (points scores minus opponents points scored). If a lineup of players is, over time, consistently outscored by the opposing lineups then this lineup cannot be considered effective.

The key question is what exactly does over time mean? One of the problems with looking at raw-plus minus scores for lineups are that they are heavily effected by small sample sizes. Especially early in the season, a good game or two can make an entirely average lineup look like world beaters.

Continue reading “How many possessions does an NBA lineup need to play before we are confident it is good?”

Usage and True Shooting Tracker

I made a web app that allows you to see how the players on each team rate according to usage and true shooting. You can quickly get a sense for how players compare to one another and can sort by team or position.  The points are also sized and colored according to a player’s offensive rating, so you can see how much better (or worse) the team’s offense has been while they are on the court. The app will be updated as the season progresses so you can always see current stats.

As a bit of explanation, usage percentage is a measure of the percentage of possessions that a player “uses up” when they are on the floor. True shooting percentage is a measure of how efficient a player is shooting the ball.  It takes into account free throw shooting and the fact that 3’s are worth more than 2’s. High usage, high true shooting players are obviously really valuable.

Try it out!


(All data is courtesy of