Since Boston’s Jan. 15 game against the Chicago Bulls, Robert Williams has been freer on defense.
Erin Clark/The Boston Globe via Getty Images
As of Monday night, no team in the NBA was hotter than the Boston Celtics. Boston had won six straight games, as well as 11 of their previous 12 and 24 of their previous 28. stab opponents by 15.8 points per game along the way as it stormed into a tie for first place in the Eastern Conference.
Boston’s overtime loss to the Toronto Raptors on Monday night might not have been the harbinger of trouble for the team as the playoffs approach, but it did offer a glimpse of at least one issue the team will have to deal with the rest of the way . Boston played without four of its five starters as Jayson Tatum and Jaylen Brown rested sore knees on the second night of a back-to-back and Al Horford missed his second straight game for personal reasons. The Celtics should have those three starters in the lineup once they get into the postseason, but they may not have Robert Williams III, who sat out the first game of an extended absence on Monday after suffering a meniscus tear in his left knee at one Victory on Sunday afternoon against the Minnesota Timberwolves.
Boston’s spectacular run was fueled by his league-best defense and, in particular, a tactical shift from coach Ime Udoka that revolved around how he used the Time Lord in his plan. For the team’s Jan. 15 game against the Bulls, Chicago was without Zach LaVine, Lonzo Ball, Patrick Williams and Alex Caruso due to health and safety protocols and various injuries, and Bulls coach Billy Donovan started Alfonzo McKinnie alongside DeMar in the lead up DeRozan and Nikola Vucevic. Udoka responded by flipping the responsibilities of Williams and Horford. Rather than let Williams defend Vučević, Udoka gave Horford that assignment and let Williams defend McKinnie.
As Udoka explained a few weeks later, “We changed some things defensively, whether we have [Williams] more off the ball, less on the ball and so he can be a defender on the assist side instead of switching as much and keeping him closer to the basket. We took him out of the basket earlier this year and that obviously took some rim protection and his comfort zone away from him.”
Prior to that game against the Bulls, Williams had spent most of his time defending opposing big men, which often meant venturing to the edge when his aim went to set a ball save. Due to the frequency with which Boston pick and rolls rotate, Williams spent far too much time outside the basket. Since that game, Williams has largely defended the opposing striker’s weaker shooter, allowing him to move more freely down the defensive line and help near the basket.
With Krishna Narsus Defensive position estimation (DPE) concept we can see the dramatic effect this tactical tweak really had. DPE is a positional average of a player’s half-court matchups (from Second Spectrum data) where each opposing player is assigned their default position value, and these values are weighted by the number of possessions the player has defended those opponents. (For example, a player defending centers (5) for 50 possessions and power forwards (4) for 50 possessions would have a DPE of 4.50.)
We calculated Williams’ DPE for each game this season and his rolling averages for the entire season and five games using matchup data from Second Spectrum. Before that January game against the Bulls, Williams had a DPE of 4.02; in the games since then it’s 3.18. In the 34 games he played before Udoka’s strategy change, Williams recorded just four games with a DPE south of 3.50; in the 27 games he played after the transfer, he only had eight games with a DPE over 3.50.
Letting Williams roam free as a backup assistant paid off tremendously as he is one of the best rim protectors in the NBA. According to NBA Advanced Stats, he converted just 50.7 percent of shots when he was within 5 feet of both the shooter and the rim — the sixth-best mark among 108 players who played in at least 20 games and challenged at least three such shots per game.
With Williams sidelined indefinitely, the Celtics will need to find a whole new way to protect the color. None of the team’s other frontcourt options come close when it comes to defending the rim: Horford has allowed a 55.7 percent conversion rate on shots near the basket; Daniel Theis approved 60.5 percent; and Grant Williams scored 65.7 percent. (An interesting twist might be putting Brown in the backline helper role. He doesn’t have great rim protection numbers this season, but he’s the only Celtics regular with the same explosive athleticism as the Time Lord.)
Boston’s defense against drives actually performed about as well with Williams off the ground (1.07 points per possession including drives, according to Second Spectrum) as it did with him in the game (1.06), but his presence served as a deterrent as opponents dared about five times less per 100 possessions. Without Williams behind them, the likes of Tatum, Brown, Marcus Smart, Derrick White and Payton Pritchard need to be even stronger at attack to prevent ball handlers from going downhill where they can either do more damage near the basket or force more (and more Panic) help so they can spray the ball outside to open gates.
Williams’ absence will also affect Horford and Grant Williams.
Horford started the season reasonably well, but saw his effectiveness dwindle during the long stretch between late December and the All-Star hiatus. He seemed refreshed after having more than a week to rest his body; But with the regular season drawing to a close, the Celtics may have more minutes to count on. Horford has exceeded 32-minute burnout just 19 times in his 64 games this season, and at age 35 he is likely more burnout-prone than 24-year-old Williams. How Horford holds up under increased stress is suddenly one of the most important questions for Boston’s season when just a few days ago it was unclear how often he would be part of Udoka’s final line-up.
Similarly, the Celtics will need big contributions from Grant Williams every night now. His third NBA season was his best yet as he dramatically improved his 3-point accuracy and he offers tremendous versatility on defense. Out of 253 players who played 1,000 minutes or more this season, Grant Williams ranks seventh on the Bball Index’s Positional Versatility metric. Playoff opponents will surely test this improved outside shooting and challenge him (along with Smart, White and Horford) to beat them with knights while paying special attention to Tatum and Brown. He’s also not quite as good at passing as Robert Williams, which could give Boston’s much-improved offensive machine a little wrench.
Without the vertical distance Robert Williams offers as a pick-and-roll threat, the Celtics’ extra perimeter players will be under more pressure to put down both their three-pointers – which could be more contested as opponents may not be as tempted , to help get deep into the paint before recovering to shooters – and make the jump when Tatum and Brown divert defensive attention away from them. Smart has once again settled in as a 3-point shooter with low 30s and decent volume, while White has only connected 25.8 percent of his Treys since he was acquired at close. White shot 34.4 percent from deep during his time in San Antonio, so he’s a better shot than what he’s shown in Boston so far, but he’s not necessarily a plus in that department.
It’s worth noting that Smart has improved as a playmaker this season while being used more often than ever as a point guard. According to Basketball-Reference.com, he’s played 100 percent of his minutes at this point this year — the first time he’s played primarily as a point guard since his rookie season.
Smart has coped well with the added responsibility (and leadership burden that comes with it) as he’s on track to reach his career-best assists per game, assists per 36 minutes, per 100 ball possessions, and assist rate. He has five double-digit assist games this season after recording just 11 such games in his career prior to this year. He seems to be making high-level reads and manipulating defenses more often than ever before, rather than reacting to them.
Horford is also a fairly capable playmaker, particularly when selecting cutters from high post, but also when working as a short roller outside of ball-screen action. He’s a very different type of pick and roll threat than Robert Williams, however, as Williams rolls hard to the basket far more often. Theis offers a slightly larger Dive Threat but in a far less athletic package, making the action much less threatening to opposing defenses. (Theis, however, is arguably the league’s top enforcer for the “Gortat screen,” where he locks down the assisting defender on a pick and roll while rolling to the rim.)
Williams is expected to miss the rest of the regular season after undergoing surgery this week. But as ESPN’s Adrian Wojnarowski reported Wednesday morning, the procedure Williams underwent — likely a meniscus removal (which entails a shorter recovery time) based on a four- to six-week return period — makes it possible he could get back on the ground if Boston has a longer run after the season makes. Even if he does, it’s unlikely he’ll be the same force he’s been this season right away. Williams has emerged as an All-Defense-worthy player this year, one who was firmly in the mix for Defensive Player of the Year. How the Celtics explain his absence individually and collectively will be perhaps the single most important factor determining their fate in the playoffs.
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