A Physicist Explains Why LeBron James's Game 3 Dunk Was So Remarkable

At this point in the NBA finals, there isn’t much hope left for LeBron James and the flailing Cleveland Cavaliers. But if Game 3 on Wednesday night was any indication, James is going out strong. In the first quarter of the game, he sidestepped the Golden State Warriors’ Javale McGee and passed the ball to himself off the backboard to finish with an epic two-hand dunk. The internet went crazy for it. The Physics of Basketball author and physicist John Joseph Fontanella, Ph.D. thought it was okay.

“I’m impressed by the process in the sense that he figured out a way to convert what is an inherently difficult shot,” said Fontanella, professor emeritus of physics at the United States Naval Academy and literal author of the book on basketball physics, in an interview with Inverse. In other words, Fontanella, unlike all of basketball Twitter, is less impressed by the dunk itself and more so with the speed with which James decided to go through with it.

From the outset, he says, James didn’t appear to have any intention of going in for the dunk: James was near the center of the paint when he shook off McGee and went in for the alley-oop to himself. “When you’re at about eight to ten feet, I’ve always considered that to be the most difficult shot in basketball,” he says. “Particularly for these big, strong guys, they’re in real close. It takes some really, really fine motor skills to drop that ball in the basket.”

All of the options a player has for shooting at a distance of eight to ten feet are difficult, says Fontanella, because to do so a player must carefully balance the power of their shot with their speed as well as their distance from the ring. At that range, options include shooting a floater, which involves releasing the ball higher up than you would for a normal layup, and a bank shot off the backboard. Both of these are hard to do.

“You’re used to shooting from long range, and now you’ve got to have this soft touch to bank the ball in,” he says. “It’s very, very difficult from about ten feet.”

Rather than go with these risky shots, James made the split-second decision to go for the self-pass, in which he skillfully bounced the ball off the backboard and caught it on his way up for the easy dunk. “I don’t think there was anything spectacular about the dunk,” says Fontanella. “It was a two-handed dunk.”

That said, dunking successfully requires maximizing certain physical components, specifically speed and momentum. In a video on dunking for SpiderTV, Christine Helms, Ph.D., a physics professor at the University of Richmond, explained: “You have to leave the floor with a certain velocity to make it to the basket.” The moment a player stops running down the court and jumps up for the basket, they must convert their lateral momentum to their vertical momentum. Doing so, ultimately, is decided by muscle strength — in particular, the muscle contractions involved in lengthening and stopping, said University of Richmond strength coach Jay DeMayo in the video.

Ultimately, the dunk was made possible because LeBron James is LeBron James, and combining quick decision-making, great aim, impeccable timing, and an already-immense vertical leap generally comes easier to one of the most athletic players to ever grace the NBA. “His makeup of muscles and the like are unparalleled,” says Fontanella. “Purely and simply, it’s [his] vertical leap. If you can’t jump, you can’t dunk.”