How the Boston Celtics switched their way toward an NBA championship

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The Celtics proved the old adage — “Defense wins championships’ — correct.

On the surface, it was a seemingly mundane baseline out-of-bounds (BLOB) play at the four minute and ten second mark of the second quarter that the Dallas Mavericks were priming to run. But as is true of high-stakes NBA basketball, there are multiple layers hidden beneath the supposed simplicity of an NBA possession.

When you think of how the Boston Celtics defended the Mavs throughout the course of the 2024 NBA Finals, the aforementioned possession makes a ton of sense. Against the most prolific corner shooting team in the league during the NBA season, the Celtics held the Mavericks to a total of 22 corner-three attempts (non-garbage time) in five games — an average of 4.4 attempts per game, well below the Mavs’ regular-season average of 11.3. While “pushing the right buttons” would still be an apt way to describe the Celtics’ defense when it came to limiting a typically potent offense, “flipping the correct switches” would be more apropos — both in the figurative sense and in the literal manner through which the Celtics threw a ton of switching the Mavs’ way.

The maneuver of switching assignments around a screen can be deceivingly effortless to the casual eye. It may look easy, but there are multiple factors to consider: the timing of the switch, the compatibility of the defenders involved, the possibility of counters (e.g., slipping the screen to gain separation from the switch before it can be established), and several other underlying factors at play. Ball-screen possessions are the most common switchable actions, but the difficulty is exponentially increased when switching off the ball — particularly, in a situation such as a baseline out-of-bounds set.

So when the Celtics were faced with a “pick-the-picker” (also known as a “screen-the-screener”) action during the aforementioned BLOB situation, a seemingly distant connection was made between a discussion LeBron James and JJ Redick had in an episode of the Mind the Game Podcast.

Before we delve into that discussion — and to set the stage for the connection — here’s the play in question:

Defense is often a mental-checklist exercise, which is easy in theory but difficult to pull off while mired in the fast-paced nature of an NBA possession. The best defenses in the league are neither detail insufficient nor speed vulnerable — that is, they make sure to cross every “t” and dot every “i” without the need for slowing things down. Quite obviously, their opponents won’t accommodate them in the latter regard.

If the possession above was to be made into a checklist, it would look something like this:

Stay true to the principle of taking away the corners (Al Horford was able to stay home against Derrick Jones Jr. on the weak-side corner, while Jaylen Brown successfully kept tabs on Kyrie Irving on the strong-side corner).
Make sure that neither Irving nor Luka Dončić spends considerable time handling the live ball and finishing the possession.

In those two regards, it was an astounding success. The Mavs had no choice but to feed the ball to PJ Washington, who attempted to create his own scoring opportunity but shuffled his feet due to a timely rotation by Sam Houser.

When shining a magnifying glass on the possession to deduce why (and how) every item on the list was checked off, peep at both Brown and Jrue Holiday — and attempt to understand their maneuvers while a James proposal about defending “pick-the-picker” BLOBs to Redick is overlaid:

Who would’ve thought that simply switching the inbounder’s defender would throw a wrench into the Mavs’ BLOB? But that’s exactly what Holiday and Brown do; instead of chasing Irving toward the corner, Holiday switches off of him and switches onto Dončić, whose initial defender (Brown) drifts toward the corner to switch onto Irving. Holiday’s maneuver, therefore, is to plug a gap created by an attempt to plug another gap.

With both Dončić and Irving in no position to get the ball back to create something out of nothing, Washington is forced into a role he’s not comfortable playing, resulting in a bumbling attempt to score at the rim.

If such a phrase exists that can capture the essence of what the Celtics’ defense was all about in these Finals, it’s most probably this: “Take away their best offensive options and live with the outcome produced by everything else.” Their corner three philosophy was born out of this approach: no one was allowed a corner look, especially Dončić and Irving; everyone else was allowed above-the-break looks, save for Dončić and Irving.

Much has been praised — and maligned — about the Celtics’ mathematical approach to the game. People aren’t keen on understanding the apparent difficulty of applying numbers to a game that has treated such figures as a supplementary and secondary aspect. But it’s not as hard to understand as many people think: three is greater than two, which doesn’t require an engineering degree to absorb.

But that’s a concept that applies to only one side of the ball. While the Celtics have embraced the 3 > 2 philosophy by spreading the floor and fully embracing a 5-out offense, they’ve also applied its reverse on defense — that is, two is less than three. In that regard, their philosophy is also quite simple: make opponents take tough twos in lieu of attempting efficient threes.

Again, that is where their anti-corner philosophy comes in. But it also applies to the nature of the twos they’re willing to give up, and which ones they’re not allowing.

Peep at the commonality between these shot profiles from the Mavs, per Cleaning The Glass:

Game 1: 33% rim frequency (55th percentile), 38% mid-range frequency (79th percentile), 29% three-point frequency (10th percentile)
Game 2: 30% rim frequency (42nd percentile), 39% mid-range frequency (83rd percentile), 30% three-point frequency (14th percentile)
Game 3: 32% rim frequency (48th percentile), 40% mid-range frequency (86th percentile), 28% three-point frequency (9th percentile)
Game 4: 37% rim frequency (80th percentile), 31% mid-range frequency (43rd percentile), 32% three-point frequency (21st percentile)
Game 5: 30% rim frequency (38th percentile), 24% mid-range frequency (21st percentile), 45% three-point frequency (90th percentile)

On the aggregate, the Celtics were able to put a lid on the rim while also taking away the three-point line — while also funneling the Mavs’ shot attempts toward the mid-range area. The corner three vs. above-the-break three battle was also a subplot of this overarching theme, but another notable stat that captured the Celtics’ approach: the Mavs only had a total of six alley-oop attempts in five Finals games, an average of 1.2 attempts per game. That is a far cry from the three attempts per game they averaged in their 17 playoff games prior to the Finals.

It was on the grandest stage, with the lights switched on at their brightest, that the Mavs hit the proverbial wall, courtesy of the Celtics walling off the rim and switching almost at will. If the Mavs wanted to score, they’d have to bleed for it — and no possession captures that situation with more accuracy than on a possession involving a Mavs staple half-court set.

We must once again look back to see what worked in the past:

In order to appreciate what the Celtics did to take away what victimized lesser teams:

Plenty of odes and tributes will be paid to the Celtics’ offense — how every member of their five-man lineup was every bit of a shot creator as a shot finisher, how it made defenses overexert and overstretch themselves to their utmost limits, and how it was the most efficient in NBA regular season history.

But more often than not, a top-10 defense is the deciding factor behind what constitutes a championship team. The Celtics — third in overall defensive rating during the regular season, first in half-court defensive rating — became the latest in a long line of elite championship defenses.

There was no “on” switch to be flipped, no gear to shift into. The switch was always there — in the form of, quite literally, switching their opponents into half-court oblivion.