Nylon Calculus: Is it possible the Boston Celtics are better off without Isaiah Thomas?

I know, it’s a silly question. But after the Celtics, improbably, stole Game 3 from the Cavaliers on the road, it’s been asked, a lot. Even the good dudes at Celtics Blog felt obligated to write down their answers (a pretty emphatic and unanimous no).

But even if you know the answer before you start, whether the Celtics would be better off without Isaiah Thomas is worth talking about because Boston has a lot of decisions to make about how their roster will be shaped over the next few years. Thomas will be right smack in the middle of many of those decisions, and what happens over the rest of the Eastern Conference Finals is a sample of data Boston will certainly be looking at.

If you just started watching NBA basketball this week, meet Isaiah Thomas. He’s been on an upward trajectory over the past few seasons but peaked this year in a way almost no one expected. He had one of the most efficient high-volume scoring seasons in the league, in league history really, and he was the driving force for Boston’s offense all season long. He’s also 5-foot-9 and because of his inherent size limitations an enormous problem on defense.

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ESPN’s Real Plus-Minus (an estimate of a player’s net impact per 100 possessions, based on both box score stats and plus-minus numbers adjusted to account for teammates and opponents) is not a perfect measure but it does a nice job of highlighting the imbalance in Thomas’ contributions.

Real Plus-Minus estimated Thomas to be the fifth-most impactful offensive player in the league this season, trailing only Stephen Curry, Russell Westbrook, James Harden, and LeBron James. It also estimated him to be the worst defender in the entire league. Put the two halves of his game together, the bad cancels out much of the good, and his overall net impact is estimated to be +1.60 points per 100 possessions, about the same as Patty Mills. So, consider his offense and he’s elite. Consider his offense and his defense, and the result is merely a slightly above-average player.

Thomas is an outlier from the rest of the league but he’s also an extreme outlier from the rest of his team. You can see from the graph above that most of the Celtics other rotation players grade out as positive defenders, although no one has anything close to Thomas’ offensive impact. (Avery Bradley’s rating is kind of a mystery here as Real Plus-Minus did not like his defensive performance this season, despite his strong reputation.)

As you would expect, this roster construction means the Celtics have been a much different team when Thomas is on the floor. The tables below show Boston’s offensive, defensive, and net efficiency when Thomas is on and off the floor, parsed by the regular season, playoffs, and then against the Cavaliers (with regular season and playoff games combined).

In the regular season, the Celtics were very good with Thomas on the floor — an elite offense with what would have been a bottom-10 defense stretched across the entire season. When Thomas went to the bench, their offense cratered and their overall point differential sunk, but they flipped and became an elite defensive team. Just to put that all in context, Boston’s offensive efficiency with Thomas on the floor would have led the league during the regular season. Their defensive efficiency when he was on the bench also would have led the league during the regular season.

The pattern has been a little more wonky in the playoffs — Washington really exploited Thomas’ defense in their seven-game series — but some of it holds. The Celtics were a much better defense when Thomas was on the bench. The interesting thing in the first two rounds of the playoffs is that some of their supporting offensive players also stepped up — Al Horford, Terry Rozier, Avery Bradley — and they were able to score efficiently even when Thomas wasn’t in the game.

Which brings us to Cleveland.

The Celtics did not win Game 3 because they were forced to play a different style without Thomas. Their defense was disastrous — they allowed Cleveland to score 118.9 points per 100 possessions — but they won because Marcus Smart caught fire and LeBron James wasn’t himself. Neither of those two variables really has anything to do with Thomas.

That being said, if the Celtics had to play one elite team without Thomas, the Cavs might be the perfect pick. Cleveland is exquisitely suited to targeting mismatches and their offense would find and exploit Thomas wherever he was (see the DRTG number in the table above). Cleveland’s defense is also shaky which should theoretically make it easier for Boston to score with non-Thomas lineups. To be clear, the Celtics are not better off without Thomas, but for the rest of this series Boston gets to run an experiment on that scenario.

The Celtics hold the number one pick in this year’s draft and seem likely to select a point guard, Washington’s Markelle Fultz. Thomas and Fultz could certainly play together, both in tandem or as a starter-understudy combination, but Fultz’s immensely high ceiling does call into question Thomas’ future with the team, both in the present, and as they pivot towards the future. The argument could be made that this year’s Celtics team, was a product of circumstance more than design. That is to say, the roster was heavier on potential than present fit. They leaned on Isaiah because he took a huge step forward and that was the path to winning games, not because this team was intentionally built to be supported by his strengths and weaknesses.

In thinking about whether the Celtics could be better without Thomas, the question comes down to choosing the more plausible of two scenarios. Is it more likely that Boston, through roster adjustment or internal development, figures out how to play better defense with Isaiah on the floor? Or that they figure out how to score more efficiently without him?

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Boston is lucky that there is nothing external at play forcing them to make a choice this summer. They can take Fultz, pair him with Thomas next season and see what happens. It’s hard to marginalize someone whose personality is so engaging and whose production has been so heroic for Boston this year. But if Rozier, Bradley, Smart, Crowder, Horford and the rest of this rotation can tighten defensively on the Cavs and continue to score efficiently over the next few games, it makes a compelling argument that they might not need Thomas.