Celtics became the best defense in the NBA?

While the eyes of the basketball world were focused on the off-court moves of the Philadelphia 76ers and Brooklyn Nets, who traded their superstars at the trade deadline last month, it was another Atlantic Division team that made significant moves on the court.

Despite falling to the Indiana Pacers on Sunday, the Boston Celtics are the hottest team in the Eastern Conference and are looking like the contenders many thought they would be at the start of the season. The Celtics have a 17-6 record in their last 23 games.

First-year coach Ime Udoka has turned around a team that had an 18-21 record and was ranked 11th in the East on Jan. 7, making them a legitimate threat to make the NBA Finals. How have the Celtics pulled it off? One word: defense.

Since hitting their lowest point total in early January, the Celtics have a defensive efficiency of 101.5, and that’s after giving up 128 points to the Pacers on Sunday. The Miami Heat have the league’s second-best defense in that span, allowing 107.1 points per 100 possessions. To put into perspective how much better Boston has been than the rest of the league, that 5.6-point difference is about the same as the difference between the second-ranked Heat and the 18th-ranked Utah Jazz.

The 2021-22 Celtics are playing less like the ’86 Celtics and more like the ’85 Chicago Bears, and this defense is off the charts in a good way.

Udoka and the Celtics coaches have lined up their defensive talent with some unique schemes, and the results this year have been so good that it’s fair to consider this team a real threat to come out of the East.

In a league obsessed with pick-and-roll action, the best defenses are capable of stifling those plays at the point of attack. Boston’s big, versatile defenders are perfect for that task because they have size and physicality, but also because they communicate well on the court.

The Celtics roster is loaded with impressive defenders. They have Marcus Smart (a two-time All-Defensive Team selection) and Al Horford (who earned All-Defensive Team honors in 2018). They brought back Daniel Theis and added Derrick White, who showed strong defense in San Antonio.

Boston has been the best team defending on-ball blocks during the calendar year, allowing just 0.87 points per play on direct blocks, according to Second Spectrum. This impressive mark is due in large part to this team’s uncanny ability to switch assignments at a high volume without ending up with mismatches.

Since Jan. 1, the Celtics have switched “curtains” against the ball 673 times, the second most in the NBA during that span, trailing only the Heat. Boston has given up just 0.83 points per consecutive play when switching in 2022, the best such mark in the NBA.

Consider this basic question: which team has the least efficient offense in the NBA in 2022?

It’s not the Oklahoma City Thunder. The Thunder have scored just 103 points per 100 since Jan. 1, which ranks 30th in the league. That’s the team playing Boston.

Celtics opponents are scoring just 100.9 points per 100 possessions in 2022.

Udoka has settled into a starting lineup that pairs superstar wings Jayson Tatum and Jaylen Brown with Horford and Smart along with center Robert Williams III. Few thought the 35-year-old Horford had much left in the tank, but he has played more than 1,500 minutes (fourth most on the team) and has provided Boston with exactly the kind of veteran leadership it has lacked in its frontcourt.

The return of Horford and the arrival of Udoka also paved the way for the emergence of Williams, who provides the Celtics with one of the most agile and versatile defensive centers in the league. He is the exact type of anchor in the middle that allows a team to switch as much as the Celtics do, and his ability to disrupt shots is already world-class. Williams has limited opponents to 37.8% shooting as the closest defender. That’s the lowest in the NBA this season and the second-lowest in the last five seasons by any of the 847 players who defended at least 500 shots.

He is third in the league in blocks and 14th in rebounds despite playing less than 30 minutes per game.

The combination of Horford’s veteran years and Williams’ youthful explosiveness make this frontcourt one of the best units in the league, but the two players are not alone.

Tatum, Brown and Smart are also strong and willing. There are none small or lightweight. There are no lazy defenders. The perimeter defense is also elite, and the addition of White at the deadline only makes Boston better.

It’s easy to be fooled by the standings, which show Boston at No. 6 in the East, just two games out of playoff territory. But the underlying numbers leave no doubt that this team is for real and should be taken seriously as a threat to win the Eastern Conference in the postseason. Even accounting for that disappointing start, Boston is outscoring teams by 5.3 points per game, the largest margin among Eastern teams.

The Celtics have a 19-6 record when starting their preferred five-man lineup (Horford sat out Sunday’s loss as part of a plan to manage his minutes after playing 37 the night before).

In their 322 minutes on the court combined, Celtics starters are outscoring opponents by 26.6 points per 100 possessions. Folks, that’s ridiculous. No other starting lineup with at least 200 minutes together comes close to that. That’s a better lineup than the Milwaukee Bucks (Giannis Antetokounmpo, Khris Middleton, Jrue Holiday, Bobby Portis and Grayson Allen), who are +13.2. The Golden State Warriors’ best lineup features three All-Stars (Stephen Curry, Draymond Green, Andrew Wiggins), and not even a third of what the Celtics’ starters have done.

FiveThirtyEight’s RAPTOR projection model gives Boston a 30% chance of making the Finals (better than any other Eastern Conference team) and an 18% chance of flying the flag for the franchise’s 18th NBA championship.

While the numbers scream for us to pay attention to Boston, so does recent history. Tatum and Brown are entering their prime, and Boston has now appeared in three of the last five Eastern Conference Finals (the first of which took place before Tatum was on the team).