Nylon Calculus: The westward movement of NBA talent

Even if we set aside the drama spawned by Isaiah Thomas’s physical examination, the blockbuster trade between the Boston Celtics and the Cleveland Cavaliers had many intriguing angles. It marked a major transaction among top contenders, who dueled in the Conference Finals just a few months beforehand and are likely to clash again in the 2017-18 season. It involved marquee (though flawed and polarizing) players, an underrated spot-up wing, a David Blatt protégé, and a first-round pick with roots in another landmark deal. From a front-office perspective, it pitted a rookie general manager against one of the longest-tenured executives in the NBA.

Amid these gripping plotlines was a simple yet notable detail. By trading Kyrie Irving to an Eastern Conference rival, the Cavs temporarily stemmed the westward migration of talent. The 2017 offseason had already seen the departures of Jimmy Butler, Paul George, and Paul Millsap, adding to the relative dominance of the West. At least for a brief moment, the Irving-Thomas swap resisted that trend.

We can explore these and all other offseason player movements in the graph below (click the image to enlarge):

This chord diagram displays all 30 NBA franchises alphabetically, beginning with Eastern Conference teams (orange) on the right and, moving clockwise, Western Conference teams (blue) on the left. Arc length represents total 2016-17 Real Plus-Minus wins, so the Golden State Warriors occupy more of the circle than the Brooklyn Nets do. Each line (or “chord”) shows player movement between teams. Crucially, the width of a line indicates the outgoing players’ RPM wins.

That seems rather dense, but the key is simply to focus on the thick chords that are colored differently from their originating team, which signal major player movement across conferences.

Start with the prominent blue line atop the diagram. This chord indicates the 11.5 RPM wins produced by Millsap, who switches from the Atlanta Hawks to the Denver Nuggets. If we move clockwise from there, we find Brook Lopez (7.6 from the Brooklyn Nets to the Los Angeles Lakers), Butler (17.4 from the Chicago Bulls to the Minnesota Timberwolves), George (9.7 from the Indiana Pacers to the Oklahoma City Thunder), Jeff Teague (8.1 from the Pacers to the Timberwolves), P.J. Tucker (6.0 from the Toronto Raptors to the Houston Rockets), and Patrick Patterson (5.4 from the Raptors to the Thunder). All of these players bring top-100 RPM wins from the East to the West.

On the flip side, Gordon Hayward (9.5) goes from the Utah Jazz to the Celtics. Victor Oladipo (6.9), part of the Pacers’ return for George, is the only other top-100 player traveling from West to East. Even if we count Dewayne Dedmon, whose 4.5 RPM wins rank 101st in the league, the eastward migration still pales in comparison.

Overall, accounting for every player who switched conferences, we arrive at roughly 79 RPM wins shifting to the West and about 42 heading to the East. Perhaps unsurprisingly, both the total and the net gain for the West are the highest in any offseason since the inception of the stat.

Over the past four offseasons, total RPM wins going to the West have steadily increased, as has the net gain of westward movement. In 2014, the East actually stole the show, primarily through the Cavs’ Kevin Love trade (13.5) and the Magic’s Channing Frye signing (10.8). But, since then, the West has had the edge. After a relatively mild 2015 offseason, in which the main conference switches involved Zaza Pachulia (7.7 from the Milwaukee Bucks to the Dallas Mavericks), Lou Williams (6.0 from the Raptors to the Lakers), and Deron Williams (5.5 from the Nets to the Mavs), westward migration picked up pace. The 2016 offseason saw five players with 6.5 RPM wins or more (Pau Gasol, Oladipo, Luol Deng, Jared Dudley, and George Hill) joining Western Conference teams. This year, the West went up another notch by adding All-Stars.

Of course, this is just one way of gauging the flow of player talent. You can use other metrics (Box Plus/Minus, Player Tracking Plus-Minus, Historical Box Score, Dredge, etc., or a combination thereof) as the basis of measurement. You can take advantage of multi-year rather than single-season data to reduce noise, or even rely on a predictive version of a preferred statistic. The ease of collecting and analyzing RPM wins makes it a desirable option for this article, but while it does a decent enough job of capturing what we’re after, we should nonetheless remember that new team context, age, skill-level changes, and other important factors are overlooked.

Additionally, this article is limited to players who are officially in the NBA during both the prior and current seasons. That means the arrival of talent from outside the league (including rookies) is ignored, as are departures due to retirement, overseas opportunities, etc. The omissions do not affect the analysis, though it ends up being predominantly focused on established players who move from conference to conference.

Next: Nylon Calculus -- Offseason movement and offensive styles

Even with these caveats, there seems to be sufficient evidence that the current offseason is indeed noteworthy. An already star-studded Western Conference has continued to strengthen its grip on upper-echelon talent.

Technical Note: The chord diagram was created in R using the chorddiag package, which draws from d3-chord in the D3 Javascript visualization library.