Inside the six-figure project to solve the mystery of NBA flopping

Patrick Hruby

Ken Clark did it for science.

It was 2014, and Clark, then a doctoral student at Southern Methodist University, was part of a biomechanics group tasked by Dallas Mavericks owner Mark Cuban with studying – and perhaps fixing – flopping, basketball’s dark, daffy art of fooling referees into calling fouls that aren’t.

Like all researchers, the SMU team needed data. Specifically, collision data. The underlying idea, Clark tells the Guardian, was “what if we just imagine people like billiard balls and go from there?” And that’s how Clark, his colleagues, and some hardy student volunteers found themselves in a campus lab, slamming each other off their feet, over and over again, as sensors captured every pileup.

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“I don’t want to get the lab in trouble, as far as exposing students to bumps and bruises,” says Clark, now a kinesiology professor at West Chester University in Pennsylvania, with a laugh. “But I’ll say this: the collisions were designed to replicate what goes on in a game.”

Years after a company owned by Cuban gave a six-figure grant to SMU to investigate a perpetual hoops quandary that leaves game officials perplexed and fans apoplectic – flop or not? – the school’s Locomotor Performance Laboratory has released its findings in an amusing and informative video that breaks down everything you wanted to know about the physics of flopping, but probably never thought to ask:

  • It takes surprisingly little force to knock a stationary human off balance or entirely onto their keister, even someone as large and strong as the typical National Basketball Association player – which means flopping may not be as common as people assume.

  • If a player throws their arms skyward upon contact like they’ve just crawled through 500 yards of sewage-smelling foulness to escape the Shawshank penitentiary, then yes, they’re probably flopping.

Floppers bring a distinct quality to their performances – measurable momentum – that can be used to help identify and perhaps even police the act.

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“The athletes in the NBA and college basketball are incredible,” Clark says. “But when you watch them take a hit, it’s obvious that sometimes they are positioning themselves in a way to topple with the least amount of force possible – and that’s putting it tactfully. To put it bluntly, they’re exaggerating collisions and falling down when they wouldn’t normally have to. So when are they flopping? We felt we could address that from a rigorous scientific framework.”

Everybody flops

Marcus Smart did not step on a landmine. It only looked that way. During an Atlanta-Boston game in 2016, the Celtics guard – and acknowledged grandmaster of contemporary NBA flopping – dashed along the baseline to position himself for an offensive rebound. Hawks forward Kyle Korver bumped (brushed?) Smart with his hip. Smart went airborne, knees tucked toward his chest like a platform diver, groan-gasping as if Mike Tyson had just landed a kidney shot, eventually landing somewhere in the vicinity of the basket stanchion.

Speaking to ESPN earlier this year, Smart didn’t defend his flop, which earned him a $5,000 fine from the league office. But he didn’t exactly condemn the practice, either. “Let’s get that straight, that’s a flop, this was hilarious,” he said. “I deserved everything that came my way after that. I flop on defense, your favorite player flops on offense. That’s the only difference. Especially in a game where the offense has nothing but the advantage, the defense has to do something to get the advantage back.”

Smart wasn’t wrong. In the NBA, there are two types of players. Those who have flopped, and those who haven’t – yet. LeBron James flops. Chris Paul flops. Stephen Curry flops. Hoops history’s attic is crammed with Oscar-worthy efforts: a Vlade Divac pratfall here, a Dwyane Wade tumble there, a truly magnificent offense-defense double dive from Manu Ginobili and Raja Bell, the flopping equivalent of the Al Pacino-Robert DeNiro diner face-off in Heat.

“Flops have been around for a long time,” says Ronnie Nunn, a former NBA referee and league director of officials. “We even have rebounding flops! Dennis Rodman was really good at grabbing the wrist of his opponent while going up and making it look like he was being fouled. Karl Malone introduced an arching back on rebounds – if he was closer to the basket than his man, he would make it look like he was pushed [in the back] and was being moved, even if that [opponent’s] forearm never came forward.”

Nunn laughs. “Basketball is a crafty game. In terms of fooling the referee, flopping is part of its art and culture.”

Cracking down

Flopping is also, to use a technical term, cheating. A kind of athletic Fyre Festival ticket. Basketball fans love to see the good guys get away with some well-timed ersatz contact; they get irate when the bad guys pull the same trick.

Players, coaches, and NBA front offices are no different. In 2012, the league cracked down, announcing that flops – defined as any physical act that appears to have been intended to cause the referees to call a foul on another player – would earn warnings for first-time violators, followed by an escalating series of fines for repeat offenders.

“I think flopping had a lot of [general managers] up in arms,” says Washington Wizards general manager Tommy Sheppard, who has worked in the NBA for 26 years. “It had become a weapon, and it seemed like an unfair advantage. It’s not fair. It’s not right. It doesn’t pass the eye test. So the league tried to shame people into not flopping.”

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To stop flopping, however, you first have to spot flopping – yet by definition, a good flop is indistinguishable in real time from a genuine foul. According to Nunn, separating fiction from fact isn’t always easy. Not when the game features some of the world’s most explosive athletes. And not when officials already are keeping a watchful eye on a half-dozen different things in any given moment.

Besides, not all flops are considered flops. Pretending to get hit and falling down? Verboten. Acting as though a forearm that never touched your face nearly removed your head? A no-no. But adding a dramatic physical flourish when you’re also really and truly being fouled? That’s just “selling a call” – and the NBA is fine with it.

“Embellishments are the other piece to this,” Nunn says. “Players use them to win calls they were going to win anyway. Say you have a dribbler putting his arm into the chest of a defender. The defender flailing away like the offensive player threw a punch may be less bad than the offensive player using their arm to get an advantage.”

Beyond the eye test

Enter Cuban. Curious and data-driven, he approached SMU biomechanics professor Peter Weyand in 2013 with a novel request.

Could Weyand’s lab study flopping, the better to reduce referee guesswork by creating some basic guidelines on what levels of force, speed, and size contribute to genuine falls – especially in a league where guards weighing less than 200lbs regularly bowl over front court players more than 50lbs heavier?

“If you look at a high-contact sport like football, you see few pancakes, where guys end up on their behinds,” Cuban told the Wall Street Journal at the time. “Yet in our sport, guys end up on their backsides all the time.”

Weyand and his team specialize in athletic performance – they’ve researched Usain Bolt’s unique stride, Oscar Pistorius’ artificial legs, and how to run a marathon in less than two hours. Yet when they began to investigate athletic performance art, they quickly realized it was virgin scientific territory.

“We looked at sports science related to soccer – there’s obviously a lot of flopping there,” Clark said. “We looked at the biomechanics of slips and falls in daily living. We looked all over the place. There wasn’t much out there.”

<span class="element-image__caption">Dallas Mavericks owner Mark Cuban commissioned the study into flopping.</span> <span class="element-image__credit">Photograph: Tony Gutierrez/AP</span>
Dallas Mavericks owner Mark Cuban commissioned the study into flopping. Photograph: Tony Gutierrez/AP

Facing a void, the SMU researchers began with a basic question: just how much force does it take to knock someone off balance, or completely over? Weyand’s team wrote predictive equations. They fashioned a mechanical dummy – nicknamed “Gus” – out of plywood, PVC pipes, and galvanized tubing and repeatedly knocked it down with a padded, sensor-equipped yellow bar. They used to same bar to topple lab volunteers outfitted with reflective sensors.

“I wanted to put a [San Antonio] Spurs jersey on Gus,” Weyand said with a laugh. “Maybe Ginobili or someone else known to be a flopper. But not everyone in the group would have been happy with that – it would have been pushing it little too far to put [the Mavericks’] cross-state rivals in there. No pun intended.”

All three experiments told the same story. It doesn’t take much to knock someone standing upright off balance – just 50lbs for a quarter of a second, roughly the same as walking or lightly jogging into someone.

Weyand, who played basketball at Bates College, was surprised. “If we had found that it takes huge amounts of force, then you could assume that every time you see someone falling over in a NBA game, they’re faking it,” he says. “But no – in many cases, if the defender just doesn’t move their feet, then down they go. I’ve been through thousands of charge-block collisions, and never realized how easy it was.”

Adding extra

Next came human-on-human collisions. One person got a running start. The other remained stationary. Participants wore boxing headgear and baseball catcher chest pads, and fell into a padded track and field pit mat.

“It was more fun than dangerous,” Weyand says. “We had very thick mats.”

Did anyone end up needing to wear a cup? “If someone had gotten really doubled over or took a shot [between the legs], it would have been common knowledge in the lab,” he says.

The researchers staged hundreds of collisions at different speeds, heights, and angles. In some, the stationary targets were told to react naturally; in others, they were told to flop. All of the hits were recorded using a 12-camera system similar to the ones used to create motion-capture animations for video games such as NBA 2K.

Analyzing that data, Weyand and company drew two key conclusions. First, during natural two-person collisions, the stationary recipient will fall backwards with their arms out – but not up, and certainly not high enough to direct traffic on an aircraft carrier flight deck.

“Those big, above the head gestures you see in the NBA?” Clark says. “That’s not natural counter-movement. That’s what floppers do.”

Second, the SMU researchers confirmed that human collisions are subject to the same laws of physics as billiard balls. How so? When two objects collide, total momentum is conserved – that is, the stationary object can’t gain any more momentum following the impact than the moving object loses. In flops, however, total momentum increased, a telltale sign that the floppers were adding something extra to the equation.

“Either they were jumping after the collisions, or it was excessive arm action,” Clark says. “Either way, we could measure it.”

Lasting value

Drawing on their study, the SMU group has recommendations for NBA officials – and anyone watching at home – making Flop or Not calls:

  • Make sure the defender’s body and feet are stationary;

  • Make sure actual contact has occurred;

  • Make sure the defender’s response time is appropriate – that is, that they don’t start going down before a collision, nor too late after one;

  • Check for defender arm motion that’s excessively upward.


“The main thing is just to look at what players do with their upper bodies,” Clark says. “That’s the major giveaway. Anything going on probably isn’t necessary. They’re doing it to sell it. It may still be a charge, but they are selling.”

If that all seems obvious – less Galileo championing heliocentricity than the latest concussion study confirming that getting hit in the head is bad – well, sometimes the scientific method leads to known territory.

Besides, Clark does have one potentially revolutionary idea: use data from the sophisticated motion-tracking cameras installed in every NBA arena to calculate the momentum conserved or added during questionable player collisions, the better to flag who might be flopping.

“We thought about that a lot,” he says. “They know much these players weigh, and what speed they’re moving at all times. Depending on how accurate the cameras are, you don’t need a system like we have in our laboratory to do similar calculations.”

But does the NBA need a system at all? In the first three seasons following the adoption of anti-flopping rules, the league reportedly handed out a total of 87 warnings and 13 fines to 73 players. Last season, by contrast, just five warnings and zero fines were issued.

Nunn attributes the drop to improved officiating. Sheppard says an emphasis on perimeter play means fewer low-post backdowns and rim-attacking drives – which also means fewer opportunities for traditional defensive pratfalls.

Still, neither man believes flopping is a dying art. Instead, it’s simply evolving. “Now you have more varied flops,” Nunn says, “and more flops by offensive players.” To wit: in 2017, Houston guard James Harden’s ability to draw dubious fouls on three-point shot attempts led the league to adopt new officiating guidelines.

“[Flopping] gets passed down from generation to generation,” Sheppard says. “Usually it’s peer-to-peer, but sometimes players become a coach and teaches it. It’s getting that handful of jersey, or sticking that elbow under someone’s arm, and somehow you’re the one being held or being hit. Guys that can master it can squeeze another year or two out of their careers. Setting screens, drawing fouls, getting an extra possession – that is valuable.”

Should Cuban again decide that flopping is valuable enough to research, there’s much more to study.

“The circumstance we looked at in the lab was stationary defender, offensive player coming in, the most controlled situation so we could be most certain of the numbers,” Weyand says. “But a lot of collisions on the court are not like that. You have off-ball picks, rolls with two players moving. To have firm answers to those, we’d have to [study] an actual NBA game. Is it potentially possible? Sure.”

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