Explaining 'gravity' in basketball

It's impossible to understand the way NBA offenses and defenses operate without understanding gravity. No, not the force Sir Isaac Newton discovered that keeps you from dunking without a trampoline. We're talking about the basketball version of it, the one that governs where defenders position themselves and helps determine the success and failure of offenses.

Ready to learn more? Let's break the theory down.

What is gravity?

In a basketball context, gravity is the tendency of defenders to be pulled to certain parts of the floor.

What has gravity?

Every offensive player has gravity -- but not all players have the same gravity. (More on that in a second.) Beyond them, the ball has gravity, because of the need to pressure the ball-handler and keep him from getting a wide-open shot. And the basket itself has gravity, since the highest-percentage shots tend to be taken from close range.

What determines a player's gravity?

More than anything else, the primary factor determining a player's gravity is their shooting ability. Defenders can't stray from good shooters like Kyle Korver lest they give up an open shot -- and then get chewed out by their coach. Against weaker shooters, defenders can cheat an extra step toward the ball or the paint, making it easier for them to offer help to teammates.

Crucially, though, gravity is contextual. Shooting ability is most important when players are off the ball. When it's in their hands, the ability to drive and make plays for teammates become paramount factors. Consider the difference in how a player like Tony Parker is defended with and without the ball. And location on the court also matters. A put-back specialist with limited range has almost no gravity when he plays on the perimeter, but high gravity inside the paint because of the threat he poses on the offensive glass.

The best offenses account for all of these factors, and put their players in positions where they have the most gravity. Bad offenses feature low gravity, which means poor spacing and limited driving lanes to the hoop.

Quantifying gravity

The gravity theory is simple enough, and I've been using it to describe offenses for years. Quantifying gravity to understand how it actually plays out on the court is another matter entirely. While it might be teased out of plus-minus data, nothing in the box score reflects a player's gravitational pull.

Enter SportVU players tracking. Now that cameras in every NBA arena are capturing where players and the ball are at any given moment, we can start to determine the way defenses respond to different offensive players.

Over the summer, STATS Inc. introduced a pair of new statistics utilizing SportVU data to measure the gravitational force of players without the ball. The first, named "gravity score," measures how closely the primary defender defends a player off the ball at any given time. The second, "distraction score," quantifies how much attention the primary defender gives the ball-handler.

The graphic below, courtesy of STATS, shows what each of these metrics measures for Los Angeles Clippers forward Matt Barnes. The gravity score is how close his defender (Kevin Durant) is to Barnes, and the distraction score is how close his defender is to the ball-handler (Chris Paul).

The two metrics capture slightly different versions of gravity, so our Tom Haberstroh has combined the two to create a "respect rating" that captures both measures.