Summarizing factors that influence scoring in NBA Slam Dunk Contests

In late May 2017, a colleague and I finished writing a manuscript about a study of factors influencing scores in NBA Slam Dunk Contests (SDC). We submitted the manuscript for peer review, which means that several sports analytics experts read our manuscript, pointed out its weaknesses and provided insightful critiques. Peer reviewed enabled us to produce a better manuscript. A revised version of the manuscript was recently accepted for publication in the Journal of Sports Analytics. I will summarize the findings of the study in this post. 

Let us first review what the SDC is for unfamiliar readers. I’m assuming you know what a slam dunk is. Well, the SDC is a competition of who can do the ‘best’ dunks. The definition of ‘best’ is subject to interpretation. It may be more apt to say that the SDC is a competition of whose dunks get the highest scores. Scores are awarded by a panel of 5 judges who almost exclusively give scores on a scale of 0 to 10. All the judges’ scores are added together to get a total score, usually, 0 to 50, with higher scores meaning it is a ‘better’ dunk. One contestant will do a dunk and then that dunk is scored. Then the next contestant dunks and it is scored, and so on. The highest scoring contestants in a round move on to the next round. The highest scoring contestant in the final round is declared the winner.

We focused our study on three broad factors that should influence SDC scoring:

• Dunk elements are things like where the contestant jumped from or what they did with the ball and their body while in the air.
• Contestant formatting and rules. This is things like the order that contestants dunk in, replacing missed dunks, how many rounds there are, and experience of the judging panel.
• Superlatives. Superlative factors include how popular a contestant is, having ‘home field advantage’, how unique a dunk is, and contestant height. Another is things contestants do to create excitement, usually before dunks. For example, Blake Griffin staging a singing choir before his dunk (in 2011) or JaVelle McGee having a second basket set up (also in 2011).

Compared to other judged competitions like gymnastics, there is neither an ‘official’ list of the different dunk elements that can be done nor gradings of difficulty for those elements. Indeed, there are common names for dunks like a free throw line dunk or a tomahawk. More complex dunks might have names like 360° windmill or 180° double-pump reverse. However, these names cannot easily be analyzed. This posed a problem.

So, we segmented the dunk into its elements. We split the dunk elements into [a] things that can only be done while possessing (controlling) the ball and [b] things that can be done with or without the ball. We called these primaries and modifiers, respectively. Primaries require possessing the ball and include well-known maneuvers like windmills, double-pumps, between-the-legs, and others. Two primaries can’t be done at the same time, but one can be done after another while still airborne. A neat loophole is that you could do two primaries at the same time if you’re using two balls. Modifier elements that can be done with or without the ball include things like spinning in the air, jumping from the free throw line, catching a pass, jumping over something, covering the eyes, and more. You can do multiple modifiers at the same time. Like, you can cover your eyes while doing a 360° or you can catch a pass while jumping over something. You can also do (multiple) modifiers while doing a primary, like spinning 360° and covering your eyes while doing a windmill.

Another way to think of the elements is to imagine the most basic dunk. You jump straight up and dunk the ball. Nothing else. This system of elements would call that a dunk with no primary and no modifiers. If, instead, you jumped straight up and did a 360°, the system would call that a dunk with no primary, with a 360° modifier.

With that said, we reviewed all the dunks in NBA SDCs from 1984-2016. Separately, we determined what elements each dunk contained. Twice. Our determinations were acceptably consistent. When they were inconsistent, we reviewed those dunks and came to an agreement on what elements were done. Of 682 dunks, 215 had no sourceable footage, no scores, or were missed dunks that judges scored. These couldn’t be analyzed. That left 467 that could be analyzed.

Figure 1a. 

Figure 1b.

First, we did some fancy math (i.e., logistic regression) to determine which elements are the hardest to do. (Actually, we used all 682 dunks for this part.) We used the likelihood that there would be an execution error when performing each element. Execution errors are things like misses, botched attempts, and replacement dunks. As can be seen in Figure 1, the dunk elements we would expect to be more difficult were also more likely to have errors (1a) and be classified as harder (1b).

Figure 2.

Using some even fancier math (i.e., nonparametric regression) we examined how dunk elements factored into scores. Figure 2 shows how dunk elements affect scores. The primaries are shown on the vertical axis and the modifiers shown on the horizontal axis, at the bottom. Next to each primary is a number. This is the (expected) average score for that primary when there are no modifiers. On the line next to each primary, each bar up or down represents how much the average score is changed by a modifier. Bars above the line means the scores goes up and bars below the line means a score goes done. A white line in a bar means +/- 2 points. We can see that the Basic primary, which means there was no primary, will get a low score when there are no modifiers. However, we then see that doing modifiers will increase the score for a Basic dunk with no primary. This makes sense. No primary and no modifier is the most inanimate dunk. Likewise, more difficult primaries like the between-the-legs are less affected by modifiers. This shows that both primaries and modifiers factor into SDC scores.

The dunk elements explain about 44% of why different scores are awarded for different dunks in NBA SDCs. But what about the other 56% of why dunks are scored they way they are? To figure that out, we again used some fancy math (i.e., linear mixed-modeling) to look at how contest formatting and superlatives affected scores. (Rather than use the actual dunk scores, though, we used the parts of scores that were not explained by dunk elements.)

Figure 3.

In Figure 3 we can see how contest formatting and superlative factors would affect an average dunk with the score of 45. That dunk in the initial round would be a 45, but in the middle and final rounds, it is expected to be closer to a 47. (We later show that this is due to lower scores for dunks by contestants eliminated in the initial round, so the 45 is really only for weaker dunkers.) Likewise, 3 botched attempts or 3 replacements is expected to lower the score of the dunk by about 1 point. Histrionics are things contestants do to create excitement, usually before the dunk. Although many uses of histrionics do not affect the execution of a dunk, histrionics increase scores by nearly 3 points! While we can’t tease apart if the most popular contestants are also the most athletic, popular guys like MJ and Vince are expected to get about a 2-point increase in the score—so the 45 becomes 47. If a 6’6” tall contestant and 5’7” contestant do the same dunk, the shorter contestant would be expected to get the 45 and the taller guy would get a 44. Figure 4 shows how dunking later in the order in the initial round greatly increases scores over dunking first or second in the order.

Figure 4.

Overall, the contest factors, superlatives, and dunk elements together explain about 72% of why different scores are awarded in NBA SDCs. This is a pretty good amount to explain considering that we are not saving lives or anything.

A main finding of our study was that scores go up when there is excitement surrounding a dunk. Popularity and ‘home court advantage’ yield higher scores. Scores are slightly reduced the more judges have judged and the more times a dunk has been done, which is perhaps a case of ‘show me something new’. Scores also go down when there are botched attempts or replacements—this might be a spoiler effect. Singing choirs and bouncing cheerleaders boost scores. We speculated that this was due to excitation transfer. For example, imagine you rated some potential dates on how sexy they are. Excitation transfer happens as you will likely rate them to be sexier after you get off a crazy roller ride than after you walk down a small hill. The roller coaster ride gets you excited, and your excitement is transferred to how you rate your potential dates. Judges get excited by choirs and cheerleaders and their excitement is transferred to scores.

But what does this study mean for dunkers? First—well, try not to go first in the initial round! You should try to do creditable dunks you can make on your first try. So, practice, practice, practice a set of respectable dunks so you can make them. You want these dunks to be effortless for you, like singing Twinkle, Twinkle Little Star. Anyone could sing it at a different tempo or in a loud bus station and never miss a word. You want to be able to do your go-to dunks on wood or blacktop, indoors or out, on a slightly higher rim, or in a crowded half-court space.

Likewise, the scores for the most common primary elements—windmill/cradle, double-pump, and between-the-legs—differ only by 1 or 2 points, between 44 and 47. So, although you can probably do that between-the-legs (see Aaron Gordon in 2017), doing a windmill or double-pump may get you a high enough score to progress to the next round or win. Doing things like catching a pass, spinning in the air, jumping over things, jumping from farther away, covering your eyes, and so on, will likely make up the 1- or 2-point difference between, say, a windmill and a between-the-legs. Lastly, get the crowd involved before you dunk. Do something to create some excitement. Dance. Show us how short you are compared to the height of the rim. Bring that kid with his dad in the third row out to throw you a pass.

Summarily, this is for the dunkers. The NBA SDC competitors of course, but more so for those elite athletes who excel at and train to dunk. They aren't in the NBA. Me? I’m 5’11 and I’m getting old. I can’t dunk anymore. My coauthor, who is the same height, but is several years younger, contends he can still dunk. Okay, maybe I could still dunk on a warm day when I’m well-rested and there's curvy Honduran women courtside wearing sundresses pretending not to watch. Even when I could dunk with ease though, I could never do what the dunkers do. But dunking saved my life. So, I've got to help move the sport forward in the ways that I can. One of my life goals is to be able to (almost) dunk at 40. I’ve got a few years before I get there. To 40, that is. A more important goal to me is seeing a Slam Dunk Contest in the Olympics. For the World to appreciate it. Unfortunately, that cannot happen with how winners are currently decided in dunk contests. In closing, this research was the first step of a much larger effort to legitimize dunk contests as a competition.