Inside The Numbers Of The Boston Celtics’ Historic Playoff Defense Entering NBA Finals

The Boston Celtics are heading back to the NBA Finals for the first time in 12 years. In similar fashion to their 2008 and 2010 runs through the Eastern Conference, they have leaned on their brilliant defensive schemes and veteran expertise.

Led by head coach Ime Udoka, Boston’s halfcourt defense put on a masterclass in each of the last two matchups, sending home the 2020 and 2021 East champions in consecutive series.

When they needed to buckle down and get consistent stops, the Celtics turned into a nightmare that even the well-prepared Erik Spoelstra couldn’t seem to counter.

Just in the last six games, Boston put together some of the most suffocating stretches you’ll see in the modern game.

When looking at regular season and playoff defenses, it’s always important to contextualize any metrics. Given how much the sport has changed in the last 20 years, what constitutes a great defensive game today wouldn’t necessarily be the case in the mid-2000s, before three-point attempts started skyrocketing.

For this reason, evaluating defenses from different years is extremely difficult. It’s best to know what the league-average offensive numbers were for each season, just to paint a better picture of what was expected on a per-possession basis.

Over at Cleaning The Glass, their database for offensive and defensive ratings goes back to the 2003-04 season, when the Detroit Pistons formed one of the stingiest and most tenacious defensive teams in NBA history. They also include league-average metrics, allowing us to understand whether or not a team performed up to the standard.

Digging into the database of defensive ratings, I decided to look at playoff teams to see if the 2022 Celtics are doing anything unprecedented. Then, since Boston advanced to the Finals, I realized it would make sense to filter out any team that didn’t at least reach the Conference Finals. If you don’t advance past the second round, it’s hard to warrant a seat at the table.

So, that’s 76 total playoff defenses over the last 19 seasons included in the table below – with their defensive ratings in the halfcourt, the league-average number for that playoff run, and the “relative rating,” which is how far above or below the league-average defense that particular team was during their run. The lower number, the better.

Boston’s halfcourt production doesn’t just stack up well with great, modern defenses. It’s actually off the charts, ranking first in relative defensive rating since 2004:

Through 18 playoff games, the Celtics have held opponents to just 86.8 points per 100 halfcourt possessions. In terms of raw data, it wouldn’t be a top-25 mark among the conference finalists shown above.

However, comparing it to playoff defenses in the same year, Boston is actually 9.1 points per 100 possessions better than the 2022 league average. Not only is it currently the top-ranked halfcourt defense for any team to reach the East or West Finals since 2004 … but it’s not exactly close.

As of now, the two teams under them are the 2006 Heat (-6.9) and 2017 Warriors (-6.8).

In 2006, en route to the Finals, Miami locked down the Detroit Pistons in the East Finals by limiting them to just 80.6 points per 100 in halfcourt settings and 100.0 in transition (league-average for transition opportunities in 2006 was 126.3). They were led by legendary head coach Pat Riley, who just witnessed Boston do similar damage to his Heat nearly two decades later.

Relative to the current league, it’s still shocking they are sitting above those vaunted 2017 Warriors. To many, including myself, Golden State assembled the greatest team in basketball history during the summer of 2016 and completely backed it up with their on-court performance.

It’s worth pointing out the context of who Golden State played in the Finals that year. They were lined up against another offensive powerhouse that might just be one of the best teams to not win the title. The 2017 Cavaliers were an unguardable force that nobody could really handle. After all, LeBron James and Kyrie Irving decimated the East playoffs during that run – Cleveland outscored teams by 15 (!) points per 100 halfcourt possessions before meeting Golden State in the Finals.

So, adjusting for competition, it’s easy to see why the 2017 Finals didn’t help Golden State’s defensive metrics.

Only looking at this year’s playoff teams, the Celtics have been far and away the best defensive unit.

In fact, the No. 2 playoff defense was the Chicago Bulls (a tiny sample-size of five games), holding the Bucks to just a 91.5 offensive rating in the halfcourt. Milwaukee still blitzed Chicago by a 73-point margin, though, because Giannis is inevitable in transition.

Among the conference finalists, Miami is second to Boston. During the Heat’s run against Atlanta, Milwaukee, and Boston, they held their opponents to 92.7 points per 100 in the halfcourt – a terrific defense, but still 5.9 points worse than Boston.

The Celtics’ path to the NBA Finals was unique for a variety of reasons, most notably the level of star talent they had to go through. In the first round, they swept the Brooklyn Nets in what could be considered the “closest” sweep of this era. While it may sound insane to frame it that way, we’ve never seen a team as gifted offensively as Brooklyn lose every game despite shooting 54.7% from two and 42.2% from three.

For the Celtics, the first round might have been the easiest series, but it was the toughest halfcourt offense they faced up to this point:

vs. Brooklyn:

• 116.9 points allowed per 100 possessions
• 97.6 in the halfcourt
• 58.1% effective field goal percentage allowed
• Nets turned it over on 16.1% of their possessions
• Nets shot 42.2% on 27.3 three-point attempts per game

vs. Milwaukee:

• 102.2 points allowed per 100 possessions
• 81.9 in the halfcourt
• 46.7% effective field goal percentage allowed
• Bucks turned it over on 13.1% of their possessions
• Bucks shot 27.9% on 29.1 three-point attempts per game

vs. Miami:

• 103.5 points allowed per 100 possessions
• 85.6 in the halfcourt
• 47.3% effective field goal percentage allowed
• Heat turned it over on 13.6% of their possessions
• Heat shot 30.0% on 34.7 three-point attempts per game

The defensive pressure Boston put on Kevin Durant and Giannis Antetokounmpo in the first two rounds was nothing short of spectacular, and they essentially dared both Brooklyn and Milwaukee to beat them with their ancillary pieces. Neither could. Unfortunately for the Bucks, their best pick-and-roll ball-handler was out for the entire series as Khris Middleton was nursing an MCL sprain.

In the East Finals, the Celtics gave Jimmy Butler multiple looks. They started the series in traditional drop coverage against all of Miami’s ball-handlers, allowing too many open pull-ups in Game 1. Then, they adjusted to more switching, until Butler roasted smaller defenders, such as Derrick White and Payton Pritchard, too many times.

Eventually, Boston settled on a more effective hedge-and-recover approach, not gifting Butler the switches every time. Although it’s taxing to execute and requires high-level timing, the Celtics used it to wear down Miami and burn the shot clock on most possessions. It didn’t help the Heat to have their second-best shot creator, Tyler Herro, sidelined for Games 4-6 with a groin injury, then only utilized for six minutes in Game 7.

Can you point to the health of Boston’s opponents in the last two rounds as a reason for their historical defense? Possibly. It’s only fair to acknowledge the injury situation.

At the same time, you play who’s in front of you. Nobody is going through the list of top-tier defenses of the last 20 years and pointing out various injuries that could’ve swung the outcome.

What we can say, however, is the Celtics are about to get their strongest test. After a brutal stretch of 12 games in 22 days, they needed the last few days off before walking into San Francisco to take on the three-time champs.

Golden State’s offensive flow, prowess, and pure intelligence are on vastly different levels than Milwaukee and Miami. After game-planning for bigger wings in Butler and Antetokounmpo that can storm through you and shoot over you, the film session is now dedicated to a sharpshooting phenom – one that never gets tired, doesn’t even need the ball to tear your defense to shreds, and already has 28 Finals games under his belt.

No other basketball player has seen more defensive coverages than Stephen Curry. Boston won’t give him anything new to figure out. But they will be the most physical, aggressive, and switchable defense he’s faced in a series.

We’ll see if the Celtics can keep this special run going and complete one of the best playoff performances of this era.