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Zone Defense Saved Duke’s Season Until It Ended It

The most talented and athletic team in the nation turned to a 2-3 scheme to protect its two biggest stars. But now Duke’s super freshmen have more questions about their defense than answers.

AP Images/Ringer illustration

Duke was the most talented team in college basketball this season. The Blue Devils had Grayson Allen back for his senior season, and they surrounded him with the best recruiting class in the country, with four of the top eight recruits in ESPN’s Top 100, including two surefire lottery picks in Marvin Bagley III and Wendell Carter Jr. Coach K won a national title in 2015 with a team built around two one-and-done lottery picks (Jahlil Okafor and Justise Winslow), and he had the pieces to do it again. There was one key difference between the two teams, though, which reared its head in Duke’s 85–81 OT loss to Kansas in the Elite Eight on Sunday. Duke played zone full-time this season, something no national championship team has done in 15 years, since Syracuse in 2003.

Even the best zone leaves open spots on the floor that a well-coached team can exploit. Kansas, which may not have a single player taken in the first round of the NBA draft, doesn’t have nearly as much individual talent as Duke, but the Jayhawks are a smart and experienced group with numerous shooters and playmakers. Using a zone against a team like that is playing with fire, which is what made Coach K’s decision so unusual. Zone defenses are usually run by teams without the size or athleticism to guard their opponents. The Blue Devils don’t fit that profile. They started five blue-chip recruits, all of whom are NBA prospects. So why were they playing a defense that put them at a disadvantage against a less talented team?

A team that started big men as long and athletic as Bagley and Carter should have been able to play good man-to-man defense. Few players with Bagley’s size (6-foot-11 and 234 pounds) have ever had his quickness or leaping ability, and he averaged eye-popping numbers (21.0 points and 11.1 rebounds a game on 61.4 percent shooting) this season. Carter played in his shadow, but he’s a more well-rounded offensive player who has steadily risen up draft boards the past few months. Most of the questions about both players when it comes to projecting them to the next level are on the defensive side of the ball, particularly guarding the pick-and-roll in space. Coach K may have been playing zone precisely so they wouldn’t have to answer them in college.

Duke became a different team when it went to the zone exclusively, following an 82–78 loss to UNC on February 8. The Blue Devils had a 19–5 record before the switch, but most of those wins had come against the softer, nonconference portion of their schedule, and they had lost three of their previous four games. The Blue Devils were starting to resemble the teams headlined by Jabari Parker and Rodney Hood in 2014 and Jayson Tatum and Luke Kennard in 2017, elite offensive groups whose defensive weaknesses prevented them from making it out of the first weekend of the NCAA tournament. That changed when they went to the zone, as they finished the regular season on a 6–1 tear against ACC teams, with their only loss coming on a buzzer-beater against Virginia Tech.

According to the tracking numbers at Synergy Sports, Duke spent 50.1 percent of its defensive possessions this season in man and 49.1 percent in zone. The Blue Devils were significantly more effective in the latter:

Duke: Man-to-Man vs. Zone, by the Numbers

Defensive Style Possessions Points Per Possession Allowed Percentile Nationwide
Defensive Style Possessions Points Per Possession Allowed Percentile Nationwide
Man 1,288 0.845 77th
Zone 1,282 0.801 91st

Part of the issue was their youth. Allen was the only upperclassman in their rotation. Bagley and Carter were joined in the starting lineup by fellow freshmen Trevon Duval and Gary Trent Jr., and the only two bench players who got consistent minutes (sophomores Javin DeLaurier and Marques Bolden) were big men who barely played last season. The zone simplified their defensive responsibilities since players no longer had to track their man and the ball. It’s hard to teach defensive principles to such a young group, particularly one made up of players used to coasting on defense at lower levels of the game.

But that doesn’t make it impossible. Young NCAA teams anchored by elite recruits upfront have been able to play championship-caliber defense in the past. Kentucky won a national title in 2012 with Anthony Davis at center surrounded by freshmen and sophomores; three years later, they went 38–1 with Karl-Anthony Towns in a similar situation. Duke was able to win the national title that season with Okafor at center thanks to a midseason change that improved their defense. Coach K slid Winslow from the 3 to the 4 and played four good defenders around Okafor to hide him on that side of the ball. Krzyzewski had been using zone in stretches this season, and he must have realized by February that the only way to hide two poor defensive big men was to play it full-time.

There are two games from earlier in the season that should worry NBA teams when evaluating Bagley and Carter. The first was an 89–84 loss to Boston College on December 9, and the second was an 81–77 loss to St. John’s on February 3. Neither Boston College (19–16) nor St. John’s (16–17) was good this season, but both played NBA-style offenses with multiple 3-point shooters spacing the floor around the pick-and-roll. Their guards sliced up Bagley and Carter off the dribble. Shamorie Ponds of St. John’s had 33 points on 12-of-23 shooting against Duke, while Ky Bowman and Jerome Robinson of Boston College combined for 54 points and 11 assists on 20-for-35 shooting. Neither of the two Duke big men could contain dribble penetration, and they both struggled as the help defender on the back side of the play.

The biggest issue for Bagley in those games was his defensive awareness, as it has been all season. While he has the foot speed to get down in a stance and stay in front of smaller guards on the perimeter, he doesn’t have the length (at 6-foot-11, he has only a 7-foot wingspan) or the instincts to consistently rotate over and protect the rim. Bagley can be an elite individual defender when he’s locked in, but that rarely happened this season. His incredibly poor NCAA block percentage (3.8 percent) for a big man with his athletic ability is a good indication that he will not be able to anchor a defense at the next level.

Bagley’s defensive issues make it difficult to fit him into a role on an NBA team. He would be an incredible rim runner in a pick-and-roll offense, but those players are typically also asked to control the paint on defense. If he’s playing as a power forward and not as a center, he will have to become a more perimeter-oriented player on both ends of the floor. These are the same issues that have plagued Julius Randle in the NBA, and it took almost four seasons for Randle to hit his stride with the Lakers after they took him with the no. 7 overall pick in 2014. He has excelled since moving into their starting lineup halfway through the season, but it’s still unclear whether his issues as a floor spacer mean he would be a better fit coming off the bench for a playoff team.

Carter has the opposite problem. With a 7-foot-3 wingspan and a respectable block percentage of 7.6, he’s a much better interior defender than Bagley, but he doesn’t have the same type of foot speed. While Carter is fairly athletic for a player his size (6-foot-10 and 259 pounds), he’s not in the same category as freakish physical specimens like Bagley and Deandre Ayton. He’s a below-the-rim player who does most of his defensive work before a play starts by anticipating what the offense will do and positioning himself correctly. He fouled out of the game on Sunday when he slid over and tried to take a charge on Kansas guard Malik Newman rather than challenging him in the air.

Carter isn’t as much of a defensive liability as Okafor. However, he’s not Al Horford either, a player he’s often compared to because of his offensive versatility. Horford was an elite athlete in college, not the more lumbering player he is now. Big men tend to gain weight and fill out as they age, and Horford weighs 15 pounds less than Carter, despite having more than a decade on him. It’s hard for a center with Carter’s physical profile to anchor a defense in a league getting smaller and faster every year. He will need to transform his body to have any chance of chasing smaller and faster players around the 3-point line.

The rise of the spread pick-and-roll has made the transition to the NBA a nightmare for young big men. Almost every team in the league these days spreads the floor with four and five 3-point shooters in order to generate more shots from the two most efficient areas of the floor: at the rim and behind the 3-point line. The center has to defend more space than in any other period in league history. Not only do they need the speed to move as quickly as possible from Point A to Point B, they need to be able to process information quickly enough to make snap decisions. Hesitate at all and they are doomed.

Even the best defensive big men need significant reps in the NBA before they are able to translate their production from college. Towns combined the athleticism of Bagley and the instincts of Carter into one package without any of their weaknesses, and he was still a defensive liability at the next level for two and a half years. Since both Duke big men will be starting from a significantly lower point than Towns, it will likely take them much longer to become even adequate NBA defenders, and their ceilings are much lower. They will have to throw away almost everything they learned at Duke, since they spent the last two months guarding spots on the floor instead of individual men.

It’s easy to point the finger at Coach K for not teaching his young big men the finer points of defensive positioning, but that’s not something any coach could do in a few months. A college coach in the one-and-done era doesn’t develop those players for the NBA — he just tries not to screw them up. I thought this quote from Kansas coach Bill Self last season, when he was asked about whether his coaching staff would try to work on Josh Jackson’s jumper, was one of the most revealing things anyone in his position has said on the subject:

“Now can [Jackson] tighten it up and do some things differently? Absolutely. But that will probably be on somebody else’s watch. That won’t be on our watch as much. I don’t see a reason why when you have a young man for a very brief period of time why you want to totally cloud his brain with something other than very, very few, simple things.”

A coach can’t make a player bigger or faster in one season, and they can’t dramatically improve a player’s skill set. All a coach can do is put that player in a position to impress scouts by giving him a role where he can put up big stats on a good team. That’s what Coach K did with Bagley and Carter. He realized they wouldn’t be able to anchor a man-to-man defense, so he hid them in a zone. While the zone ultimately cost the Blue Devils against Kansas, they wouldn’t have been within one basket of the Final Four without it. He held up his end of the bargain with his star recruits, both of whom will be taken in the top 10. Bagley and Carter were shielded in college from the professional world they are about to enter. It will be up to the NBA team that picks them to figure out how to teach them man defense.