Isaiah Thomas’s Defense Is About To Become A Big Problem


The past forty-eight hours have been a dream for Celtics fans. They beat the Wizards to go to their first conference finals since 2012, got the right to draft Markelle Fultz, and are preparing to play a spoiler to LeBron.

Quick note: yes, it will be Fultz. Fultz plays on offense like James Harden did at Arizona State, his ability to snake the pick-and-roll with no viable roll men is elite, he is already ready to be an NBA point guard, and he uses his athleticism to be a dominant transition threat. On top of that, Markelle’s aforementioned athleticism in combination with his 6’10 wingspan make him an elite perimeter defender. For people concerned about how Fultz fits in with this win-now Celtics team, calm down, and look to how Brad Stevens used Evan Turner before this season. He is simply a better player than Lonzo Ball and comes with less baggage.

Back to the topic at hand, yes, it has been an outstanding few days for the Celtics. But, it is probably time to temper expectations for how they will perform against the Cavs, and that’s because of one main reason: Isaiah Thomas’s defense.

Specifically, the Celtics’ most important player is also a statistically horrendous defender. Thomas has the worst defensive real plus-minus amongst NBA point guards. And for people who dislike ESPN’s proprietary statistic, Thomas also has the lowest defensive box plus-minus and a completely average defensive win shares percentage.

Yet, the advanced stats do show that Thomas has been able to be an elite contributor due to his offense. I.E., while his defense resembles discussions of “white flags” at the Hague Conventions, Isaiah’s offense has been so elite that he can be the best player on a top-seed in the Eastern Conference.

Furthermore, through the first two playoff series, Isaiah Thomas’s defense has not been a problem. So why, then, will it be the Celtics’ biggest problem against Cleveland?

The answer comes in the form of one simple statistic: per Synergy, Isaiah Thomas gives up  1.52 points per possession when guarding drives to the basket, the NBA’s worst number since 2010. Further, when you watch Thomas defend, the reasons are clear: first, he does not have the lateral quickness to stay with penetrating guards; and second, he does not have the strength to make up for his lack of lateral quickness.

In the first clip, DeMar DeRozan takes advantage of Thomas’s lack of foot speed, drives past him quickly, and then scores on a mismatch against Kelly Olynyk. In the second clip, moreover, Matthew Dellavedova uses his strength to simply power through Isaiah Thomas and score.

This is a problem because the Cavs have LeBron James and Kyrie Irving. The latter of whom averages 1.338 points per possession when he drives right (Thomas gives up 1.714 points per possession when the ball handler drives right), which – for players who have driven right to the basket at least twenty-five times this season – ranks as the third best in the NBA behind Kevin Durant and Jimmy Butler.

As one sees from the clips above, Thomas really has no hope of defending Kyrie Irving when the latter drives on the right side towards the basket. Consequently, Isaiah Thomas will not guard Kyrie Irving. More than likely, he will defend some combination of J.R. Smith, Iman Shumpert, and Kyle Korver.

Yet, that is not necessarily an effective solution against the Cavaliers. The Warriors tried the same solution to the same problem during the 2016 NBA Finals. They hid Stephen Curry on whoever was the off-guard and let Klay Thompson guard Irving. The Celtics will apply this same strategy and use Avery Bradley, Marcus Smart, and possibly Terry Rozier to guard Kyrie, while Thomas hides on the off-guard.

The Cavs will attack this in one of two ways. First, when the off-guard is J.R. Smith or Kyle Korver, the Cavs will force Thomas to concede his ability to fully contest a shot.

In the above play, J.R. Smith passes the ball to LeBron James at the elbow. Steph Curry has two choices: he can leave LeBron James in single coverage with a spread floor; or, on the other hand, he can briefly double James and force him to give the ball up to Smith. Curry chooses the latter, however because Smith has a lightning quick release, he is able to shoot the ball before Curry can recover. In this scenario and unlike Curry, due to Thomas’s limited height, he will not be able to even remotely contest the shot.

Consequently, the Cavs will use these plays to create open looks for J.R. Smith and Kyle Korver. Boston could respond by having Thomas stick with his man, but that will leave LeBron in single coverage. The Pacers tried this in the first round and it was not effective.

So, ultimately, given Thomas’s limitations, Ty Lue will run plays that will result in an open LeBron dunk or an open three-point shot for one of Cleveland’s shooters.

Additionally, there is a second way Cleveland can attack Thomas, which is by having the off-guard set a screen for Kyrie or LeBron. The Celtics are not as “switch-happy” as the 2016 Warriors were, however, Isaiah Thomas has ended up defending 196 switches this season, which is not a paltry number. Furthermore, regardless of the opponent’s intention, the Cavs tend to run the same screen over-and-over or use the strength of J.R. Smith in order to force the switch. This was the key way how Cleveland attacked Curry during the 2016 Finals.

Thus, while Brad Stevens will definitely try to protect Isaiah Thomas from Kyrie Irving and LeBron James, it is unlikely that any strategies will be successful. This means that the Cavs will be able to create easy shots for their two best scorers, and consequently, that the Celtics’ best player may not have much of a positive impact on the floor.

Two brief counterpoints. First, plenty of guards are bad defensively while still being positive contributors to their team, including Isaiah Thomas, Stephen Curry, Kyrie Irving, Damian Lillard, and James Harden. And second, this specific weakness has not harmed Boston whatsoever in either of their first two playoff matches.

The response to both points, though, is that the difference is the aforementioned players are not guarding Kyrie Irving and LeBron James surrounded by elite three-point shooters for every game. This flaw creates statistical noise in the comparison. Sure, during the regular season those defensive limitations are hideable, but this has less validity against Cleveland. Chicago and Washington do not have nearly the offensive firepower as the Cavs do, and it will likely be impossible for Boston to adjust.

Overall, I still think Boston may win one game early in the series. If Cleveland is rusty for game one, or the Cavs have one of their “chill mode” games, it is very possible the Celtics can dominate. But ultimately, it seems unlikely to me that the Celtics can accomplish much more than that when their best player is such a defensive liability against this Cleveland offense.



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