We’re in a golden age for NBA offense. Teams are scoring 110.1 points per 100 possessions during the 2018-19 season, according to Basketball-Reference.com — a full 1.3 points per 100 possessions more than the previous high of 108.8, which was set two years ago.
This is largely — and rightly — credited to the boom in 3-point attempts. While the 3-point line was instituted all the way back in 1979, it took the league nearly four decades to realize that 3 was worth more than 2.1 The threes have also been complemented by other leaguewide changes, all of which have been widely recognized as contributing factors in the age of offense: a dramatic shift toward “Moreyball” shot distribution that limits inefficient shots like long twos; several waves of rule changes that opened up the floor and allowed for more freedom of movement; the increase in pace; and the sheer unstoppability of the league’s very best offenses.
In all those explanations, though, one factor has gone wildly underdiscussed: Teams just don’t turn the ball over all that much anymore. In addition to being the best overall shooting season of the 3-point era, the 2018-19 campaign also has seen teams commit turnovers at the lowest rate they ever have, as just 12.6 percent of possessions leaguewide have ended with the offense giving the ball away to the defense in one manner or another. This is down from a high of 15.8 percent during the 1982-83 season.
But while the genesis of the other offensive changes can be neatly traced, the decline in turnovers is a bit more puzzling. In my search for an explanation, I figured it was best to ask a person whose teams have mastered the art of avoiding turnovers: Gregg Popovich, whose San Antonio Spurs own the lowest turnover rate in the NBA this season (which doubles as the fifth-lowest rate since the league began tracking turnovers) and have finished with a better-than-average turnover rate in 14 of the past 15 seasons — a time during which they have the league’s fourth-lowest turnover rate overall. Popovich, though, was also stumped (or perhaps just characteristically cagey). He didn’t really have any idea why his teams have avoided turnovers so consistently, nor why the league has done a better job in recent seasons.
“I’m not even sure I know the answer to that, to tell you the truth,” Popovich said. “We don’t do any ‘don’t turn it over’ drills or anything like that. We talk a lot about decision-making and time and score on the clock, understanding your role, staying within your abilities, all those sorts of things. So, I think over time people realize how valuable the basketball is, and we just go from there.”
There are many potential explanations for the drop in turnover rate, all of which may be working in concert. The increasing prevalence of pull-up three-pointers limits opportunities for players to cough up the ball — if the ball never passes the three-point line, a turnover is far less likely as most turnovers tend to happen in more crowded areas of the floor. Switch-heavy defenses have resulted in more isolation plays, and isolations are often the play-call of choice in close and late situations because they are less likely to result in turnovers.
Regardless of why, the impact of turnovers cannot be undersold. Popovich is onto something when it comes to the value of the basketball. It makes intuitive sense: You can’t score if you don’t have the ball.
To gauge the impact of turnover rate on NBA offense, let’s look at how it’s changed compared to the other so-called Four Factors of Basketball Success popularized by noted basketball statistician Dean Oliver in his seminal book, “Basketball on Paper”: effective field-goal percentage, offensive rebound rate and free-throw rate. When looking at each of the Four Factors year over year, we can see just how stark the drop-off in turnovers has been over the years and how it compares with the changes in the other factors, all of which have followed similarly consistent trend lines.
During the 3-point era, only offensive rebounding has experienced a larger percentage change, with the rate of boards offensive teams have grabbed off their own misses falling from 33.5 percent 40 years ago all the way to 22.9 percent this season. Oliver pegged turnover rate as being responsible for 25 percent of the variance in offensive efficiency and offensive rebounding for 20 percent, though subsequent detailed analyses have typically settled somewhere around 22 percent or 23 percent for turnovers and 15 to 18 percent for rebounds. So given that avoiding a turnover is considered more valuable than grabbing an offensive rebound, it could be argued that the change in turnover rate has fully canceled out the decline in offensive rebound rate. We can see this more clearly when we weight each percentage change by the amount ascribed to each of the Four Factors by Evan Zamir’s 2010 analysis that updated the weight each factor had been assigned by Oliver.
Turnover decline is even bigger than it seems
The percentage change of Dean Oliver’s Four Factors weighted by their impact on the game, 1980-2019
|EFF. FG %||turnover %||OFF. REB. %||FT %|
The respective declines in turnovers and offensive rebounding are nearly even, while the bump in shooting efficiency far outweighs the decline in free-throw rate. Add it all up, and you’ve got a leaguewide offensive rating that is 4.6 percent better in 2018-19 than it was during the 1979-80 season (110.1 points per 100 possessions compared with 105.3 per 100).
Shooting (and shot distribution) have been talked about ad nauseam over the years, while numerous observers have noted that teams are increasingly prioritizing getting back in transition defense over chasing offensive rebounds. As ESPN’s Zach Lowe explained in 2016, the Spurs were among the first teams to deprioritize offensive rebounds, with former Spurs assistant and current 76ers head coach Brett Brown once noting that Popovich did not care if a player didn’t grab a single offensive rebound during his entire career. Pop’s lead was followed by coaches like Doc Rivers, Erik Spoelstra, Stan Van Gundy and Rick Carlisle, and with those coaches’ assistants now all over the league like Popovich’s are, it’s perhaps not surprising that offensive rebounding is down all over the place. Without the decline in turnovers offsetting that prioritization, though, we likely would not be living in the best offensive environment in the modern history of the NBA.
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