Americans can be slow to adopt European approaches, so the NBA’s halting embrace of the zone defense is not surprising. But since a rule change 14 years ago it’s become an increasing part of teams’ arsenal, and zone principles are now key in defending the pick-and-roll, the league’s primary offensive scheme.

For years, the NBA outlawed zones, forcing players to either guard their man or double the man with the ball. Any player caught guarding an area and not a man would elicit a technical foul shot.

Though it was invented in America and used in high school and college basketball, the NBA long looked down their nose at zone defense, seeing it as a tacit admission of inferior talent.

“I personally grew up thinking zone defense wasn’t allowed in the gym,” says New York Knicks coach Derek Fisher.

But in the 1990s, coaches developed strategies to abuse the man-to-man. Teams would isolate their best scorer in the post with his teammates as far away on the other side of the court as possible, to make it hard to double. “People used to put guys in the parking lot,” Fisher jokes.

This was the heyday of back-to-the basket players like Mark Aguirre and Charles Barkley, who’d back their man down for seconds at a time, slowing game action to a crawl.

To get the game moving again, the league initiated new rules limiting physical contact and lifting restrictions on zone defense. These days, all that remains of the once byzantine illegal defense rules is a stricture against standing in the lane without guarding a man for more than three seconds.

“It’s changed a lot,” says Fisher. “One of our assistants, Jim Cleamons, has a saying: a good man is a zone, and a zone is a good man. They all tend to shake out into the same thing.”

Loosening the rules has allowed the best defensive minds to develop tough double-team schemes where players rotate their assignments. Led by coaches like Tim Thibodeau, formerly of the Bulls, teams have developed hybrid man-zones that flood the ball-side and leave two weak-side defenders covering three guys. It bets the defenders can rotate faster than the offense can move the ball.

“It’s made your weak-side defense better, and it’s made it harder for people to get to the rim,” says Detroit Pistons coach Stan Van Gundy. “You don’t see quite as many [isolation plays] because of that.”

These rules changes, in concert with the increased use of three-pointers, has moved the game in the direction of the free-flowing style Europeans have played for years.

It’s no coincidence that the last three NBA champions outside of LeBron James-led teams (whose game more mimics the old-school one-on-one isolations days) employed aspects of this international style.

This included lots of zone (2011 Dallas Mavericks), a ball-movement, pass-heavy approach (2014 San Antonio), and taking an inordinate amount of three-point shots (2015 Golden State Warriors). Two of those teams featured significant players that cut their teeth in international play.

Last year two successful coaches came over from Europe. Like Rick Carlisle’s Mavericks, David Blatt’s Cavaliers toy with straight-up zone defense in addition to the popular man-zone hybrids.

“The rules are different and it makes use of zone much more selective,” says Blatt. “There are a lot of forms of it; you just don’t see it in its purest form here. But I think as the game develops and people’s grasp of it deepens you might see more or variations of it.”

Players have responded to the rule changes as well. Mirroring their pro heroes, high school and college players are modeling their games to succeed in this new environment, developing skills to suit the evolving game.

“You see so many young kids with size developing face-up games that include the ability to drive and shoot from distance,” says Eric Flannery, who won a gold medal two years ago helping coach top US high school players internationally with USA Basketball.

In fact it’s gone so far in that direction, it’s actually raised the value of youngsters with a back-to-the-basket post-up game, like last year’s third overall choice Jahlil Okafor. It’s become that much more rare.

“There just aren’t that many of them out there any more,” says Cavaliers GM David Griffin.

There’s a sort of feedback loop where, as the players become more versatile offensively, so too must the defenses. This is also why so many NBA teams favor players able to guard multiple positions defensively.

It’s all part of making those hybrid zone defensive rotations work as seamlessly as possible. And so basketball’s tactical defense race continues.

“Players are so good now [that] teams devise ways to take advantage of how you’re defending them,” says Fisher. “You definitely need to zone some things up defensively in order to cover all the things teams will do.”

It’s certainly opened up the game, and has been a boon even to someone like Van Gundy, who entered the league long before the rules changed.

“You can do a lot of things on the weak side that you were not able to do when I came into the league in 94,” says Van Gundy. “All in all it’s probably made the game better.”