Breaking Down Boston Celtics’ Defensive Scheme
Zone defense, switches, and versatility.
Truth be told, I missed out a lot in basketball. I was occupied by American Football, with the season still running in November when the NBA kicks in until come February when they topped it off with the Super Bowl.
It’s not that I don’t follow basketball entirely, but it feels like there are things that I should’ve known but I got distracted, and when I get to know about it later it’s already been too late. I watched one or two games of Celtics basketball in a month at least, and social media do the rest for me.
Just when I got the time to focus on basketball real-time, COVID-19 happens. Yikes.
But then again, every cloud has a silver lining. Despite being limited in knowledge, with all the time I have I’d like to catch up and put up something about how my favorite team in the northeast fared by breaking down a certain aspect (yes, you might’ve read the title) of their performance this season and try to look ahead on what it could be if the season continues.
Alright, let’s go through the numbers.
There are multiple ways to evaluate a team’s defensive performance by statistics, and one of them is by looking at their defensive rating numbers since it’s a commonly used metric that incorporates all the actions that happened on the court defensively (blocks, steals, and defensive rebounds).
Defensive rating can be interpreted as a number that represents the points allowed by a player per 100 possession. You can check out how Dean Oliver calculates the number and how to convert it to teams' defensive rating here.
The Boston Celtics are fourth in teams’ defensive rating with the point of 106.2, with the Lakers, Raptors, and Bucks up ahead respectively. This number is supported by the fact that they did well in preventing points in multiple situations and forcing turnovers.
As mentioned before, you can justify defensive ratings by looking at other defensive situations that are also explained in numbers. Celtics are third in points scored in the paint and fourth in points scored off turnovers, with 43.2 and 14.6 respectively. This is mainly because they also did well in restraining the opponents to make good shots as shown in being ranked seventh in opponent’s effective field goal percentage of .510.
In forcing turnovers, they are well within the top-10 of the league. Celtics forced 13.6% turnovers in defense, which is seventh in the league. As steals and blocks are the main actions we should look at while assessing turnovers, the Celtics are seventh and sixth on those with 8.3 and 5.6 per game respectively.
So, how the Celtics are pulling this off? By looking at the few games I watched this season, they did well in spacing the floor and switching on defense, forcing their opposition to move the ball around, chewing the clock. Here’s an example of how the Celtics’ chew the shot clock by playing a man defense while keeping their space tight:
Celtics started off with a man-to-man look. As Joel Embiid tries to play in the post, Jayson Tatum stretches his stance a bit just in case Ben Simmons plays it directly to Embiid while also keeping his distance to Tobias Harris.
Simmons passed it to Harris, so Tatum presses him knowing Embiid is on an island with Enes Kanter. Notice how Jaylen Brown moves a bit closer toward the dunker spot on the help side to prevent a drive to the middle.
When the ball reaches Embiid for a post-up, Simmons runs into the paint and try to beat Gordon Hayward physically. Celtics keep their man-marking as Kemba Walker follows Josh Richardson and Tatum guarding on Harris, while Brown is ready to help if Simmons makes a move towards the spot.
As the clock keeps ticking, Joel Embiid makes his move to the rim. Celtics know the Sixers don’t have much time left so they keep the middle congested to make it hard for Embiid, but it leaves four players wide open in the perimeter. Unfortunately, Embiid is fast enough to kick the ball out.
You have to give credits to Jaylen Brown for being blazing quick on closing out Al Horford, forcing the pass to Harris. This might look like an open shot, but notice that there are Walker and Tatum within reach.
A closeout by Walker forces Harris to go right, just to meet Jayson Tatum. Harris then passes the ball to an open Richardson, but it was all too late. Shot-clock violation.
Now let’s look at how the Celtics switch in an overtime thriller against the Klaw-powered Los Angeles Clippers in February:
Landry Shamet and Montrezl Harrell are in a pick-and-roll situation and the Celtics respond with a drop coverage. Celtics are eighth (75.9 percentile) in pick-and-roll defense. Good enough to be in the top-10, but not elite. Tatum got Kawhi Leonard, Gordon Hayward on Lou Williams, and Marcus Smart marking JaMychal Green.
The first switch occurred. In this particular game, the Celtics are focused on guarding frequent ball-handlers with their best defenders. In this case, Smart and Tatum are the ones who deliver the strategy. Smart and Hayward switch their man, and Leonard going to help his teammate.
It becomes clearer in this snap that the Celtics are now in 2–3 zone defense. Each player keeps their distance well and Enes Kanter is ready to face the pick-and-roll as Harrell looks like he’s on the move to help Leonard with a screen from the right side.
The Clippers are going with a double-screen, trying to pin down Smart and Tatum so Williams can operate down the court. Watch the next sequence as it’s going to be interesting.
The Celtics knew it’s going to be a pick-and-roll. Kanter drops in the coverage as Tatum did a great job fighting the screen so Williams has to turn around further to avoid steals, but watch Marcus Smart smartly (pun intended) identify the play and leaves Leonard to help.
With the help, Smart nullified the backdoor cut that could’ve been an easy basket or a one-on-one situation that can be finished with a mid-range floater. This forces the Clippers to reset the offense with no much time left.
As the shot-clock winding down to three seconds left, Harrell tries to put a screen on Smart so Leonard will have an open look but unfortunately Smart able to fight it off, which leaves no choice for Leonard to look for another option.
With two seconds left and Tatum closing in, it’s a missed shot. Celtics won the ball back.
According to Second Spectrum matchup data by Krishna Narsu, Boston Celtics are third in versatility rating average, behind Houston Rockets and Toronto Raptors respectively. And how they play in this possession justify the numbers, especially after looking at how Smart and Tatum handled the situation.
Marcus Smart is not a high-volume player with a lot of minutes under his belt, but he always gives 100% when he’s on the court and it shows in the play above. The all-defensive first-teamer earned his creds by being a matchup nightmare, putting massive efforts in defending multiple positions on the court.
Based on the matchup data Smart is putting great numbers in advanced defensive metrics like FiveThirtyEight's very own Defensive-RAPTOR (1st), ESPN’s Defensive Real Plus-Minus (3rd), and Defensive PIPM (4th) for players who are listed as guards and guarding all four positions except center at least 15% on his defensive possession.
As impressive as he has been offensively, Jayson Tatum has become a defensive monster on the defensive end for the Boston Celtics in his breakout season. Tatum surpassed his records of rebounds, steals, and blocks per 36 minutes and per 100 possessions from previous seasons. Tatum ranked first in Defensive Real Plus-Minus for players listed as forwards per the matchup data.
Bear with me as I will explain another defensive play that correlates to the aforementioned numbers, taken from a matchup against Utah Jazz in a few weeks after:
Against a team with one of the tallest center in Rudy Gobert, Celtics have to find ways to negate interior threat and they did it by using a 2–1–2 zone defense. In this play, Rudy Gobert will move to the left dunker spot and Joe Ingles will put a screen on Tatum.
In response, Kanter drops to cover Gobert and he assigns Grant Williams to guard Donovan Mitchell…
… Which gives us a kind of 3–2 zone look with Kanter sticking to Gobert. Having two men closing in on him, Mitchell has no choice but to pass to Ingles…
… Who then passed it to Jordan Clarkson, who shoots a contested three and missed it as Marcus Smart closes in on him. Utah did well in rotating the ball, but look how the Celtics keep their inside congested albeit having Gobert who theoretically can win in a post-up battle against Enes Kanter. This is an example on how they keep their opponent from scoring easily in the paint, with great spacing and quick switches.
With all being said, let’s not forget that Celtics have two players within the top-15 of versatility rating in Jaylen Brown and Gordon Hayward, a surprisingly decent center in Daniel Theis who ranked eighth in ESPN’s Defensive Real Plus-Minus, and solid rotational players like Grant Williams and Semi Ojeleye who can put up a fight and stand on their own ground, even when facing the toughest of challenges.
It wouldn’t be fair if we don’t single out the weaknesses in the Celtics’ defense. Obviously there are reasons why they aren’t ranked #1 and one of them is in rebounding.
Boston Celtics are not within the top-10 when it comes to grabbing boards. And this leads to another logical problem. If they can’t get defensive rebounds, it means the opponents are bullying them in board-grabbing battles which leads having them score on second-chances.
This is a missed shot by Kyle Lowry, although having Gordon Hayward on the ground (in Hayward’s defense, he is tripped). Celtics have three players near the paint, so it should be an easy board to grab. Knowing Rondae Hollis-Jefferson is outnumbered, Serge Ibaka comes to help. Ibaka should know it’s going to be a tough fight since Enes Kanter is directly in front of him with acres of space.
But the result says otherwise. Kanter barely making it alive on the battle and it’s a second-chance point for the Raptors.
In the same game, it’s a missed three-point shot by Fred VanVleet. Chris Boucher has the upper hand due to Daniel Theis’ awful positioning and he is in pole position to grab the rebounds. Look at what happens next.
Despite having FOUR players in the paint against THREE opponents, the Celtics embarrassingly lost the rebound to the shortest player in Kyle Lowry. Theis lost his focus as he navigates the ball, Tatum did not fight hard enough to get to the paint, and Gordon Hayward mindlessly looking at the disaster with no intention to help. Two points Toronto.
In this game, the Celtics 97–113 to the Raptors and racked up 31 rebounds, the least so far in the season compared to the 53 rebounds Toronto had.
Having an all-defensive first-teamer, a two-way rising star, and flexible players who can guard multiple positions and have a knack of how to keep their space makes Boston Celtics one of the most respected teams when it comes to defense.
The Celtics are able to keep their paint area congested when it comes to fending off teams with interior threats with good spacing and quick switches, and when it comes to defending the perimeter their players can close out sharpshooters and lock their down with good one-on-one defense.
Should the NBA continues come July and they want to compete for the title, rebounding is something they have to work on. They are considerably awful in that department and it shows as they allowed too many second-chance points. If things didn’t go out to plan, they can look for interior defender talents in the next draft pool or focus on signing a reliable big man through a trade or in the free agency market.
