The Celtics’ on-ball defense is the NBA’s most menacing pest

Arguably the most impressive defensive sequence of this impressive Boston Celtics season came at a time that couldn’t have been any more inconsequential. The Celtics led the Utah Jazz by 27 points in a game they would go on to win by 28, but you could’ve fooled Payton Pritchard. He picked up Jordan Clarkson full-court and remained embedded in his shirt for the next 15 seconds, working through one Hassan Whiteside screen and forcing one terrible pass that resulted in a turnover. He was then met at midcourt by Marcus Smart, Boston’s Keeper of Vibes, to cap off the vibiest play of the season.

But really, these sorts of plays have become run of the mill — ho-hum, really. Pressing with a 27-point lead? I mean, why wouldn’t he? He’s a member of the Boston Celtics, is he not? What else would he be doing?

This kind of effort is fascinating to watch, particularly given how lackadaisical and unenergized this same team looked just three months ago. But it’s not the same team. Only in name is this Celtics team at all similar to the one that was losing every other game back in the waning days of December. In its activity on both ends, prowess, and its ability to embarrass even the best of squads, the Celtics are a different team.

What’s been most fascinating to watch is how they’ve changed their approach on the defensive end, particularly when defending the ball. Think of the most aggravating teams you used to play in high school or on the AAU circuit; the teams that used to unabatingly shout “BALL BALL BALL BALL BALL” when defending the dribbler. That team is these Boston Celtics, sans the prepubescent squeaks meant to distract offenses from performing the most procedural tasks.

Boston has flipped the script on its 2021-22 campaign thanks in large part to the tenacious and dogged defensive effort of... well, its entire rotation. Marcus Smart, Robert Williams, Derrick White, Jayson Tatum, Jaylen Brown, and all the rest have pushed the Celtics up from ninth in the league in defensive rating (107.5) before Jan. 1 to the best defense in the NBA since the start of the new year (104.3). No one wants to play them. It’s hard for most teams to keep up with them; practically none of them can right now.

Principally, it’s Marcus Smart and Robert Williams manning the charge. Both are Defensive Player of the Year candidates — if I had a vote, it would be an unbiased and resounding one for Smart. Smart’s maintaining a career-high in defensive win shares (3.3); Williams has the league’s fifth-best defensive rating (103.2). Smart, in particular, has had an undeniable impact when defending some of the NBA’s most undeniable talents. In Boston’s March 3 game against the Grizzlies, he defended Ja Morant on 27 partial possessions, per ESPN’s Kirk Goldsberry; Morant took just three shots on those trips.

Both have helped spur the Celtics’ starters to become the league’s most devastating defense. That fivesome has held opponents to 94.8 points per 100 possessions and 31.3 percent shooting from three, per Cleaning the Glass. They’ve played the fourth-most minutes of any group of five this season, in which they are a whopping plus-24.3.

And though it’s Smart’s defensive acumen that is the team’s motor, it’d be unfair to sidestep Derrick White’s effort, as he has arguably been Boston’s most incessant (and effective) on-ball defender since his arrival at the trade deadline. His feet are rarely not moving; he’s a textbook arm-flailer; his defensive slides are staccato in nature. If he fails to stay in front of an opponent, something has gone terribly wrong. White has struggled as a shooter since arriving in Boston, but he more than makes up for things in Boston’s standard man-to-man sets.

For the season, he’s defending 12.7 shots per game, third-most on the Celtics; his opponents are making just 5.7 of those attempts. That amounts to a defensive field goal percentage of 45, the fifth-best mark on the team behind Williams, Payton Pritchard, Al Horford, and Jayson Tatum.

White has been even better — for the most part — in Boston’s last seven games, six of them wins. When limited to players he’s guarded for 1:30 or more, he’s defended a total of 45 shots, 23 of them ending in made baskets. But that number is skewed by a pretty significant outlier: the game against Oklahoma City, in which White played his second-most minutes as a Celtic and the Thunder couldn’t miss for the better part of the second half. Take away that one game, and players have shot just 41.7 percent overall (10/24) against White over the course of Boston’s 6-1 stretch. He’s been especially impressive against some of the game’s most solid bucket-getters, holding Spencer Dinwiddie, Jordan Poole, Bones Hyland, and Donovan Mitchell to a combined three-of-12 from the field. Consider the clamps on.

One of White’s better attributes as an on-ball defender is how, even when he appears to have been thwarted, or his opponent seems to have created enough space for a clean shot, White makes up ground by becoming as long as he possibly can. Shifty guards who believe they have plenty of time to get a shot off following their step-back move are routinely disappointed thanks to White’s deceiving 6-foot-8 wingspan, which he utilizes to its maximum effect. Suddenly, an otherwise customary jumper has turned into an inefficient, ill-advised shot, even for the best of shooters.

But you’ll notice that even when White and his contemporaries get beat, they have plenty of backup, most often coming in the form of Williams and Horford. That duo is averaging a combined 3.6 blocks per game, the most combined rejections of any frontcourt duo in the league. On attempts taken inside six feet from the rim, players are shooting 52.1 percent from the field when defended by Williams (12th in the league among the 324 players to play in at least 40 games) and 54.8 percent when contested by Horford (33rd). Both White (31st), Tatum (35th), and Aaron Nesmith (39th) also rank within the top 50. In short, teams are impossibly frustrated by challenging the Celtics at the rim. For Boston, it isn’t much of a challenge at all.

In contrast, they’re making life a living hell for their opponents. In four of their last seven games, the Celtics have held the opposition to sub-100 points while scoring more than 110 in six of those seven. They’ve scored 18.6 points off turnovers per game over that span, the sixth-best average in the NBA. As the saying goes, the best offense is a good defense. The Celtics are proving it to be true with every passing quarter.

What Boston has essentially done is turn a disappointingly average defense into the most-feared defense in the league; it’s a historic turnaround. If it continues through the rest of the regular season and however deep the Celtics advance into the playoffs, the team itself will become historic. I’ve never been able to fully buy into the idea that “defense wins championships.” If the Celtics end up shocking us all by turning in what was once a disaster of a season for one that ends with a trophy, I’ll never doubt it again.

What’s more? Thanks mainly to their defense, it’s not crazy to view a championship as a real possibility.