NBA Playoffs Small Sample Efficiency Check: Boston Celtics
It took the Celtics longer than expected to beat the Hawks, but that hasn't dimmed their title chances
The Boston Celtics have quietly been the best team in the NBA all season. After starting the season 21-5, the Celtics coasted to a 57-25 record, a league-best +6.5 net rating, and if it weren’t for a 4-7 record in overtime games, they likely would have finished the season with the best record in the league, with an outside chance of reaching 60 wins. Even though the Celtics have most of the hallmarks of a title favorite, Vegas wasn’t convinced, and I don’t blame them.
The Celtics’ first-round series against the Hawks was a microcosm of their season. There were stretches where they looked like the best team in the league, shrouded by far too many prolonged spells where they appeared to be coasting. A +5.3 net rating isn’t awful, but when maybe the best team in the league plays a perfectly .500 team, you expect another level of dominance. Ultimately, the Celtics took care of business with little fuss, unless you’re an Atlanta-based Janet Jackson fan, and moved another step closer to the NBA Finals.
The Celtics’ Offensive Metrics, Concerns, and Optimism
The Celtics’ offense was dynamite against the Atlanta Hawks. Their 120.3 offensive rating across six games is the third-best of the playoffs and not far off their 118.0 regular season rating. While the Celtics probably won’t continue to hit 40.6% of their 3-pointers, they did finish the regular season shooting 37.7% from distance and have shown the ability to hit 40% of their threes for an extended period. Over the Celtics’ first 22 games, around the length of a Finals run, they converted 40.8% of their threes, and in 24 games from February 6th to March 30th, they hit 39.4%. It might not be too smart to bet on the Celtics continuing to hit so many threes, but it also wouldn’t be terribly stupid.
It should be noted; the Atlanta Hawks aren’t exactly the stoutest of defensive teams. Their regular season defensive rating of 116.3 was in the bottom third and well below the league average of 114.8. In many respects, the Celtics played to the level they showed in the regular season, which is fantastic because they had the second-best offense in the league.
The shape of the Celtics’ attack didn’t budge much either. They shot the lights out, took care of the ball, didn’t grab many offensive boards, and channeled Ebenezer Scrooge by avoiding the charity stripe.
One area where the Celtics’ did see a noticeable drop is in 3-point attempt rate. They went from taking 48% of their shots from three to 43.3%, but that was a good thing against the Hawks because of what those lost threes were replaced with. The Celtics turned nearly all their lost threes into shots three feet and closer to the rim.
If it weren’t for a decline in field goal percentage 0-3 feet from the rim (73% to 71.7%), the Celtics’ shooting numbers would have looked even more impressive. Once again, the Hawks’ defense is the chief culprit. The Hawks allowed the second-highest percentage of opponent field goal attempts 0-3 feet from the rim (29.8%) but were the tenth best at defending them (68.9%).
The only area of concern for the Celtics is their hyper-reliance on hitting shots. Without gaudy offensive rebounding and free throw generation, their offense cannot weather a poor shooting night. However, the Celtics were without Robert Williams III for much of the season, which gives their offensive rebounding more upside than their regular season numbers suggest. With Williams on the court, their offensive rebounding percentage rose from 21% to 25.8%, but he only played 824 minutes all season.
Something to monitor closely is that the Celtics’ dismantling of the Hawks came without high-end contributions from their two stars–Jayson Tatum and Jaylen Brown. While it seems insane to say that two players who averaged 27.2 and 26.7 points per game on true shootings of 57.9% and 61.4% weren’t high-end contributors, the advanced metrics think both were well below their regular season norm.
Tatum saw his offensive box plus-minus (OBPM) drop from 4.8 in the regular season to 3.0 in the playoffs, and Brown saw his drop from 1.5 to 0.1. Most of Tatum’s drop is explained by a slight dip in 2-point efficiency (55.8% to 54.4%) and a significant decline in free throw generation (11.1 to 5.8 free throw attempts per 100 possessions). Nothing in Tatum’s shot profile would point to a drop in free throws, as his percentage of shots ten feet and in increased from the regular season. It’s possible the refereeing was slightly at play, as the Hawks and Celtics finished tied for 14th and 16th in playoff free throw attempt rate.
Brown is routinely viewed as maybe the most overrated player in the NBA by metrics, and I can’t fault them for it. He’s a high-volume scorer who is a low-volume 3-point shooter and free-throw generator. Throw in poor assist numbers and a concerning amount of turnovers, and it’s no surprise he routinely grades out as well below All-Star level. I think metrics like OBPM underrate the value of being able to hit a contested mid-range jumper late in the shot clock, but I do think they do a good job valuing how costly his passing and ball security are. Against the Hawks, Brown coughed up 21 turnovers to only 18 assists, which is how a player who scored 26.7 points per game on a 61.1% eFG% can muster an offensive rating of 109.
The good news is that Tatum and Brown are way better than what they showed against the Hawks, but the bad news is they still haven’t shown it in the playoffs. As long as Brown and Tatum get right, which they should when Tatum’s free throw generation normalizes, and Brown’s vase-induced wounds heal, the Celtics’ offense will rarely skip a beat.
The Celtics’ Defensive Metrics, Concerns, and Optimism
As the Celtics’ offense ran rampant, their defense kept the Hawks in the series. One of the reasons the Celtics were quietly the best team in the league this season is that no one stopped to notice that they had an elite defense. Their 111.5 defensive rating was the third-best in the league, and they did it with one of the most fundamentally sound units. They had the third-best defensive eFG% (52.8%), the third-best FT/FGA rate (.180), the best defensive rebound percentage (78.5%), and the 26th-lowest TOV% (11.3%). The defensive game plan of forgoing turnovers in pursuit of preventing everything else has been the Bucks’ defensive blueprint for ages, and it’s usually the right tradeoff to make.
So how did the Celtics see their defensive rating balloon from 111.5 in the regular season to 115.0 in the playoffs? They lost their edge on the defensive glass.
A 3.6% drop in defensive rebounding is massive at the NBA level. To put it in perspective, the Spurs and Trail Blazers finished tied for 24th in defensive rebounding percentage at 74.9% this season. The Hawks were a good offensive-rebounding team, finishing eighth with a 25.1% ORB%, and the playoffs have seen a higher ORB% than in the regular season (25% to 24%), but it is somewhat concerning that the Celtics saw a defensive strength become a weakness.
However, the Celtics did a good job limiting Clint Capela on the glass, the Hawks’ regular season leader in ORB%, and most of their uptick was seen by perimeter players grabbing more offensive boards. It could be as simple as the Celtics’ guards needing to box out better or plain bad luck, but if the Celtics do have a weakness on the offensive glass, it looks like it’s coming from the perimeter and not the interior.
All told, the Celtics’ defense, much like their offense, looks relatively unchanged from the regular season. The Hawks posted a 116.6 offensive rating during the regular season and saw their efficiency drop by 1.6 points. Another factor to consider is the Hawks’ midseason hiring of Quin Snyder. Following Quin Snyder’s insertion as head coach, their offensive rating improved from 115.9 to 121.6 over their final 21 games, and their ORB% skyrocketed to 29.5%. Snyder has a long history of constructing elite offenses in the NBA, and it’s likely that the Hawks’ full-season offensive metrics, which were already excellent, undersold what the Celtics faced.
I like to keep things simple, and trust regular season net ratings, as long as Donovan Mitchell isn’t on the team. The Celtics were the best team in the NBA by regular season net rating, and they showed in round one it was no fluke. They handled a far more dangerous Hawks offense than they were given credit for and posted elite offensive numbers despite some struggles from their two stars. This is the deepest team in the NBA by a mile, which gives them an incredible margin for error. Their reliance on 3-pointers provides a little more volatility than your doctor would suggest if you have a heart condition, but I think anything short of a trip to the NBA Finals would be a disappointment.