In the 1962 NBA season, Cincinnati Royals point guard Oscar Robertson averaged 30.8 points, 12.5 rebounds, and 11.4 assists per game. That’s a double-digit total in three of the five major statistical categories,^{1} otherwise known as a ‘triple-double.’ Robertson was the first player in league history to average a triple-double over the course of an entire season. It was a feat which many thought would never be achieved again. It seemed unbreakable. Averaging 10 assists per game is extremely difficult by itself — adding on 10 rebounds per game makes it borderline impossible. Especially because the types of players who are most likely to get 10 assists are also the least likely to get 10 rebounds. Yeah, Robertson’s record was never going to be matched.

So we thought. Russell Westbrook became the second player in NBA history to average a triple-double for an entire season in 2017 when he won the MVP award with an average statline of 31.6/10.7/10.4. Then he did it again in 2018. And 2019. He did something in three consecutive seasons which many fans assumed would never be done again after Robertson’s 1962 campaign.

Needless to say, Westbrook is a special talent. But this isn’t just about him. Fans who have watched basketball over the past decade have noticed that the triple-double has become more and more common league-wide. Lance Stephenson led the NBA with 5 triple-doubles in 2014. Seven players beat that mark last season. Three players have already done it this year. Eleven players had at least one triple-double in 1999. Twelve players have already notched one this year. There’s plenty of ways to illustrate it, but the point is clear. The triple-double is simply not as rare as it once was.

So … why? Why did the frequency of triple-doubles suddenly explode after 2015? This is a question that has been asked for and multiple possible explanations have been posed. I’m going to go through every theory I can find and see if I can find any evidence for or against it. Let’s start with the one I see most often.

#### Theory One: Faster Pace = More Possessions = More Stats

One of the most common theories is that the pace of the game has increased. If true, each game would have more possessions, which gives players more opportunities to get stats. Pretty simple.

I plotted the pace factor^{2} for each season on top of the bar graph for the number of triple-doubles for each season. The source I used to get triple-double totals only goes back to 1997 (which explains the previous graph), so I had to manually find the number of triple-doubles for other seasons. I chose to go back to 1997, the first season after the ABA-NBA merger.

From 1997 to 1990, a decrease in pace is actually correlated with an increase in triple-doubles. Of course, correlation does not imply causation and in this instance, that would not make any sense. There are multiple other explanations for the low number of triple-doubles in the late 1970s. The league leader in assists had just 8.5 per game in 1997, for instance, and none of the top passing guards were pulling down many rebounds either. There weren’t many of those versatile players like LeBron James and Russell Westbrook who regularly get plenty of rebounds *and* assists.

The graph does appear to illustrate a positive correlation between pace and the number of triple-doubles after around 2000. Less than one percent of the variation in the number of triple-doubles is explained by the pace of the game from 1977 to 2019, but if this time frame is reduced to 1998 to 2019, the R^{2} value goes up to 0.833. This still does not imply causation and it’s arguably arbitrary to reduce the time frame at all, but it does lend *some* credence to the pace argument.

I previously mentioned that the league didn’t really have many players who could get a high number of both rebounds *and *assists during the 1970s. Like I said before, the players most likely to get 10 assists tend to be the last likely to get 10 rebounds. In general, small point guards get the most assists and the least rebounds while tall big men get the most rebounds and the least assists. So, an increase in triple-doubles might mean that something is causing point guards to get more rebounds or big men to get more assists. This leads into the next popular theory on why triple-doubles are becoming more common.

#### Theory Two: More 3-Pointers = Longer Rebounds = More Rebounds for Guards

The concept here is simple: the league is shooting more 3-pointers than ever before. Shot distance is correlated with longer rebounds, and 3-pointers are long-distance shots, the league also probably has more long rebounds than ever before. Theoretically, longer rebounds give guards a better chance to … well, get rebounds. By the way, a long rebound just means that it bounces relatively far away from the hoop. Here’s an example:

James Harden’s 3-pointer hits the rim and bounces all the way to the free throw line where 6’0 point guard Fred VanVleet can get the easy rebound. A layup is most likely *not* going to bounce like that because it’s in the air for a shorter amount of time, so its velocity at the time of collision is less than it would be for a 3-pointer. Basic physics!

So, guards must be getting more rebounds. Right? The logic behind this claim makes sense, but I thought the same thing about my theory on offensive rebounds being more likely on 30+ foot shots than for normal 3-pointers. And I was wrong. We’ll have to prove it instead of assuming things.

First of all, is there any statistical evidence that supports the long rebound theory? Yes! In this article, Kirk Goldsberry uses video tracking data to prove that the average rebound distance increases with an increase in shot distance. The average rebound distance at the top of the key is 8.3 feet versus just 5.4 feet around the rim.

Now, let’s use individual average rebound data to see if shorter players actually tend to get longer rebounds.

Well, it certainly looks like there’s a relationship here! There does appear to be a strong negative correlation between player height and average rebound distance. Last season, the R^{2} value between the two variables tells us that approximately 66.6% of the variance in average rebound distance can be explained by player height.

Let’s summarize what we know so far. More 3-pointers are being attempted now than ever before. The average rebound distance on 3-point misses is greater than other shots. Shorter players tend to get rebounds at greater distances. Therefore, I hypothesize that an increase in 3-pointers being attempted should cause an increase in the number of rebounds for shorter players. Let’s see if that’s true.

‘Short player reb share’ is my lazy name for the proportion of total rebounds in a given season which were attributed to players less than 76 inches tall. This value does seem to have increased considerably between 2015 and 2017, as with triple-doubles. Well, the R^{2} value between the two variables is 0.595. There is a strong positive correlation between the two variables, but it isn’t enough to deduce a causal relationship. As with the pace theory, though, I think our evidence does provide *some* support for the idea that the increase in rebound distance is contributing to the rise of triple-doubles.

#### Theory Three: Players Are Chasing Triple-Doubles

We’ve all heard this one before. Remember all the lively discussions that were had during Westbrook’s MVP season? All the claims that he was just stat padding for triple-doubles. The arguments that Westbrook was only an MVP candidate due to our use of the base-10 number system. Good times. Anyway, I definitely do think that players are very stat-aware (even more so these days, maybe) and may hunt for a triple-double if they’re close to it.

Here’s the theory: If a player has double-digit points and rebounds, and 9 assists, they might be inclined to hunt for that last assist. We’ve certainly seen it happen before:

Westbrook had nine assists at this point and was hoping Steven Adams would put up a shot so he could get the triple-double. Adams chose to pass to the open man, and well, Westbrook seemed a bit upset about it. Curry and Durant found the ordeal pretty funny despite having just gotten blown out.

Anyway, back to the point. Let’s take a look at the assist distribution in games where a player has more than 10 points.

Standard stuff. Exactly what you would expect, yeah? Now, let’s add another filter. Here’s the assist distribution in games where a player has double-digit points *and* rebounds.

When a player has double-digit points and rebounds, they are more likely to record 10 assists than they are to record 9 assists. I struggle to come up with a plausible explanation for this discrepancy other than the result of players chasing triple-doubles.

Let’s do the same thing with the rebound distribution. Here’s the rebound distribution when a player has double-digit points and assists:

The discrepancy here is even bigger than in the assist distribution (probably because it’s easier to hunt a rebound than an assist). I think it’s safe to say that NBA players tended to hunt for extra stats when when they were close to a triple-double over the past three seasons.

Of course, the question is whether or not this is a new development. If you recall (scroll up!), the number of triple doubles really exploded in 2016 and especially 2017. So, let’s take a look at the rebound distribution from 2010 to 2015 when the frequency of triple doubles was ‘normal.’

Well, the stat padding phenomenon is still clearly there, although to a smaller extent. I don’t think the difference between the two time frames is not significant enough to explain the explosion in triple-doubles. Still, we were able to find irrefutable proof that players *do* hunt for triple-doubles, so that’s pretty cool!

I’ll wrap this up with one last theory. Remember what I said about there being less players in the 1970s who are capable of stuffing the stat sheets with both rebounds *and *assists? Less triple-double capable players, if you will? Well, what if we just have more triple-double capable players than ever before? What if talent is just increasing across the board?

#### Theory Four: More Well-Rounded Star Players

I’ll make this a short commentary rather than the statistical approach I went with for the other theories.

In 2019, 8 players had at least 5 triple-doubles: Russell Westbrook, Nikola Jokic, Ben Simmons, LeBron James, Luka Doncic, James Harden, Elfrid Payton, and Giannis Antetokounmpo. These are all players who are known for their ability to rack up triple-doubles. The idea behind this theory is that more of these types of players exist than ever before. After all, getting a triple double is not a possibility for every archetype. Shaquille O’Neal is one of the most dominant basketball players of all-time, but he wasn’t getting many double-digit assist games.

And if you think about it, some of these triple-double capable players have entered the league fairly recently. Giannis, Payton, Luka, Simmons, and Jokic are all 25-years-old or younger. Maybe their arrival into the league is a big part of the surge in triple-doubles. After all, a single player’s dominance can have a significant impact on the historic triple-double trends. Maybe the triple-double explosion since 2017 was literally just the Russell Westbrook effect. He *did* have 42 triple-doubles on his own in 2017.

I have mixed feelings on this theory. I do think that the talent in the league is continuously improving. However, I think that this doesn’t quite fully explain the increase in triple-doubles. I have a hard time believing that an uber athletic player like Michael Jordan couldn’t rack up more rebounds than Luka Doncic or Elfrid Payton. Of course, there’s more to rebounding than just sheer athleticism, so maybe I’m wrong. Who knows?

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