SOMETHING SEEMED OFF about Cleveland Cavaliers point guard Matthew Dellavedova during last Thursday night's game against the Brooklyn Nets.

He was held scoreless in 17 minutes of action, taking six shots and missing every single one of them, in perhaps the coldest shooting performance of his career. But if you'd looked closer, you would have found that something was indeed off -- or, to be more accurate, something was missing. In each of the prior 15 games, a wearable gadget had been strapped to the wrist of Dellavedova's guiding hand. On that night, for the first time in over a month, Delly's left wrist was bare.

The device that had been occupying Dellavedova's wrist is called a Whoop, and it's built to track fancy stuff such as heart rate, body temperature and body movement during both awake and sleeping hours. Think Fitbit, but for the million-dollar athlete. (It is not, mind you, built to help a point guard's shooting, so any correlation between Dellavedova's poor showing and the absence of his Whoop is surely coincidental.)

There is, however, one problem with it: The Whoop is prohibited under league rules.

For most of March, Dellavedova wore the Whoop (pronounced like "hoop," not "whoopee cushion") without repercussion from the league office, which bans wearable technology for use in games. Ten years ago, such a rule had little impact on the game; players had no use for velcro-ing a Blackberry on their arm. But behind the scenes, more and more teams are using hi-tech, body-monitoring devices such as Catapult accelerometers -- worn underneath the jersey, and ostensibly not during the games -- to track workloads and movement in the name of injury prevention. Catapult's client list now includes 19 teams, up from 12 last season. But while devices such as Catapult and Whoop are deemed legal for practice, games are decidedly off limits.

On Thursday last week, the league office was made aware of Dellavedova's gear and informed the Cavaliers that it would not allow the health tracker to be worn during the game. Ever since, the black strap on Delly's wrist has disappeared.

It's no coincidence that a teammate of LeBron James was wearing a Whoop. The company, a Boston-based startup founded in 2012 by Harvard graduate Will Ahmed, recently hired James' longtime personal trainer Mike Mancias as an advisor. James, a four-time MVP, dons the wearable device just like Dellavedova, but not in games.

You may have seen James' Kia K900 commercial in which he tried to dispel the Internet-fueled rumors that he doesn't drive the sedan with a $49,000 sticker price. As James sits in the driver's seat during the 30-second spot and peers into the camera, you can spot a black tracker wrapped around his right wrist. Whoop, there it is.

"At the elite level," Mancias says in a recent Whoop press release, "it's no longer just about outworking your opponents to get an edge."

On Sunday, Dellavedova confirmed to ESPN.com that he has to take off his Whoop before games now, but offered no comment. Whoop, there it isn't.

What's the big Whoop?

Chances are you, or someone you know, have worn a Fitbit or a Jawbone. According to research firm Gartner, 70 million fitness wearables were sold across the globe in 2015. With tech giants such as Apple, Samsung and Google introducing smartwatches, health trackers are having a moment.

Matthew Dellavedova's "Whoop" measured his heart rate, body movement and skin temperature for a few weeks in March. If such wearable technology is eventually legalized -- it is illegal under the current CBA -- questions remain about who owns the data. Ken Blaze-USA TODAY Sports

And while most folks haven't heard of a Whoop, it may be one of the most intriguing products used in the sport. It collects data that other devices can't; a standard Fitbit can't offer ambient temperature, recovery scores and heart rate variability. But where Whoop sets itself apart is that it is geared to change behavior, not just inform. The device delivers actionable and behavioral recommendations tailored to the user, depending on the information it receives.

From September 2015 to January 2016, Whoop tracked the user behavior of 119 athletes among eight NCAA Division I teams -- including those in basketball, tennis, swimming, and track and field. What did they find? Within that sample, the average time dedicated to sleep per night increased by 42 minutes across the four months. And the group's "sleep hygiene" improved as well; according to the study, athletes reduced their late-night caffeine consumption by 86 percent, reduced their alcohol consumption by 79 percent and reduced the use of screened devices in bed by 20 percent. Resting heart rate and heart rate variability, key biomarkers of stress, improved as well.

The upshot: Over the course of those four months, the studied athletes experienced 60 percent fewer injuries.

When reached for comment on the Dellavedova situation, Whoop's CEO Ahmed declined to speak on Dellavedova, or any specific athletes. "I think we'll see more and more athletes interested in wearing physiological monitoring tools," Ahmed said. "As athletes push toward improving their recovery, in-game wear of safe, lightweight technology becomes an increasingly important topic. Whoop strives to empower athletes to understand their bodies on a 24/7 basis. Anything less is depriving them of important knowledge."

The Australian connection

It's not hard to see why Dellavedova wore his Whoop for games. In fact, he has been groomed to find a scientific edge since he was a teenager.

At 16, Dellavedova moved eight hours away from his childhood home to the Australian Institute of Sport (AIS) training center to hone his skills. The sports science facility has been a trove of talent both on and off the court. Projected top pick Ben Simmons spent 2012 at AIS; 2014 No. 5 pick Dante Exum also spent time there. This past offseason, the Golden State Warriors and Philadelphia 76ers hired scientists from the AIS to oversee their medical, performance and injury-prevention departments. The Milwaukee Bucks hired two Australian sports scientists to their performance and medical staff.

This past summer, Dellavedova personally called P3 Peak Performance, a leading sports science institute geared toward injury prevention, and asked if he could get an assessment for this season. (He tested out as one of the best, most efficient lateral movers among over 100 NBA players).

Dellavedova, a self-described coffee junkie who gave up java during the 2015 Finals after a case of severe dehydration sent him to the hospital, is no stranger to the science of sport. "He's probably had more caffeine education at the AIS than most NBA players," said one Australian sports scientist who has worked closely with Dellavedova.

But Delly isn't the only player using the tech. On Sunday, following Blake Griffin's return to the court after almost four months on the sidelines, the Clippers star said he and his trainer habitually used a heart rate monitor around his chest to assess his conditioning levels. Heart rate is a key factor to determine player readiness and recovery.

"Instead of everyone going their separate ways, we have one spot we can go and just enjoy each other's company. It just continues to build the camaraderie that you need to be successful from year to year."

But here's the funny part about that: Professional athletes, whose very livelihoods depend on their fitness, can't wear these fitness trackers when they need it most -- on the court or the playing field. Or at least that's the case in the NBA, NHL, MLB and NFL; all four leagues ban wearables in games. (Note: This week, MLB reportedly decided to permit two types of wearables in games: a smart arm sleeve to track elbow mechanics, called the Motus Baseball Sleeve, and the Zephyr Bioharness, a heart rate and breathing monitor. But no American pro league permits wristbands like the Whoop.) As a result, Griffin didn't know where his heart rate needed to be for in-game intensity. His conditioning, therefore, was mostly guesswork.

The future of wearables

So why ban wearable trackers like Whoop, Catapult's GPS device, during games? There are a few sound reasons.

First, while wearable software may promote healthy bodies, the hardware may not. Imagine Dellavedova's wrist accidentally slamming into someone else's face and the device crashing into an unprotected eye socket. Not good. And while the devices may be microscopic or embedded in the jerseys anyway, the issues go beyond the physical realm. Where do you draw the line for which devices are allowed? Would the league's marketing partnerships govern which devices are OK'd? And who should own the data extracted from the wearables: the player, the teams or the league?

All are tricky questions, ones that, according to league sources, will be on the table during the labor talks around the next collective bargaining agreement. Those talks can come as soon as 2017. Talk to those inside the NBA and sports science industry, though, and you'll hear a common refrain regarding that CBA: the wearable issue is so new; and the business is exploding so fast; and the ethical, political and legal ramifications so thorny; it's no telling how it will be addressed.

As for Dellavedova, his actions didn't ultimately elicit a punishment from the league. Neither Delly nor the Cavs paid a price. But given how injuries have sidelined some of league's biggest stars and crippled teams, this likely won't be the last time we hear of athletes trying to minimize wear-and-tear through what they wear.