The Fundamentals: Celtics push back against roster's core limitations

Brad Stevens and the Celtics don't have superstar talent, but they are finding ways to win. How exactly? SI.com's Rob Mahoney examines.

During the second quarter of Wednesday’s game against the 76ers, Isaiah Thomas walked the ball up the floor to initiate a pet Celtics set. The play in question would have Thomas call his own number, but not before handing the ball off to Jared Sullinger at the top of the floor, dashing around a Tyler Zeller screen, setting a back screen of his own to queue a Jae Crowder cut, and then curling up the floor to tuck back behind Sullinger and receive a pass. From there, Thomas would make his move down the right wing until he was caught between two defenders: Nerlens Noel, whose primary objective in that moment was to contain him, and T.J. McConnell, his own man still in pursuit. 

Thomas played them both. He turned his shoulder as if he were doubling back in retreat, freezing Noel in the process. Then, with McConnell closing in, Thomas reversed into a jump stop toward the baseline as a setup for his jumper. The ball leapt from Thomas’s hands, floating up and just out of McConnell’s reach before finding the net.

Boston, now 8-7, relies on possessions like this one in every game it plays. Thomas isn’t just the most confident Celtic shot creator but one of few competent in the task; for all of this team’s considerable depth, the next most dependable option in generating offense might be Evan Turner. The ball, then, tends to find its way to Thomas when player and ball movement alone fail to yield an acceptable scoring opportunity.

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Most everything that Thomas does is difficult. It’s arduous work to clear enough room for a layup or runner. His shot attempts feel rushed and, frankly, why wouldn’t they? Playing a conventional style with typical timing isn’t an option for a 5'9" guard, leaving Thomas to find his own way. In this context, his most common options involve taking a difficult shot or making move after move after move in an effort to find a better one. That these possessions work at all is a testament to Thomas’s skill level. Even a game built to favor towering figures and imposing wingspans cannot contain Thomas’ guile, nor deny him the 21.2 points per game he works out against the grain. 

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One can see in that inherent difficulty, however, an emblem for what ails the Celtics. Boston is nothing if not outmatched. Brad Stevens has a wealth of options to choose from in constructing his lineups but none so impressive as to measure favorably against other starting-caliber units. Throughout the league, 30 five-man lineups have logged 75 minutes or more this season, per NBA.com. The Celtics’ sole representative—and current starting lineup —on that list ranks 29th of 30 in net rating by eating a 19.2-point deficit every 100 possessions. Roster-wide capability can’t save Boston from the fact that a great many opponents have a single lineup better than any the Celtics can offer.

In the regular season, that deficit largely comes out in the wash. Boston turns out so many quality rotation players that it tends to eat away at an opponent’s lead as a game goes on, making its biggest push in the third quarter. NBA backups are at the mercy of the Celtics’ swarming perimeter defense; Marcus Smart (when healthy), Avery Bradley, and Jae Crowder do a terrific job of applying pressure in moments of vulnerability, sniffing out any possibility of a turnover:

Even a player like Thomas, a subpar defender individually, has a role to play in scrambling to create turnovers and scooping up the lost dribbles and wild passes that result. Sullinger, Amir Johnson, and Kelly Olynyk also do fine, reliable work in their defensive positioning within Stevens’s scheme—even if they don’t finish defensive possessions on the glass as well as he might like. The balance is a formidable defensive team, through and through; after adjusting for schedule, Basketball-Reference rates the Celtics as the league’s seventh-best defense thus far.

This is a fair, representative mark for a team that plays hard, scouts well (turnovers are not made of effort alone), and has the personnel to maintain—particularly upon Smart’s return. It’s also the kind of figure that could ultimately be misleading for the purposes of playoff projection, given that teams generally invest more minutes and attention to their top lineups in the postseason. Those second-unit ball handlers that the Celtics fluster with regularity will see less time and responsibility in a seven-game series. The quirks in bench chemistry that Boston exploits won’t be as prevalent among better players at year’s end. None of this will neutralize Boston’s defense fully, though the factors in play do offer some hint of long-term concern.

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Smart, to his credit, had given the Celtics’ first five more bite in some of his more recent games as a starter. Stevens’s rotation had settled so that Sullinger and Johnson replaced Tyler Zeller and David Lee at the top of the rotation, with Smart taking Avery Bradley’s place in the starting backcourt prior to his knee injury. The offense within those lineups still churned only as far as Thomas could take it, but Smart’s presence activated something within the defense that Avery Bradley could not. The furthering for that trend could be crucial to Boston finding any kind of postseason success, particularly when considering that Thomas—and thus the entire Celtics’ offensive engine—tends to be significantly less efficient when playing against starting-caliber opponents.

Of course, we’re still dealing with small enough samples as to make dramatic contrasts in the data seem suspect. Smart is unquestionably valuable and clearly an excellent defender. That the same base starting lineup with him in place of Bradley, who also does great work in coverage, would be almost 19 points per 100 possessions better on defense doesn’t track on film. The real contrast between those two lineups is likely distorted by noise in this case, though their relative truth is still very much the same: Boston is at best using its starters to get by, an approach less feasible in any isolated game of import.

As of now, the Celtics are a good team that can be rather clearly overwhelmed by quality opponents—and, on occasions like Wednesday, pushed to the limit by terrible ones. Yet any conversation of Boston’s prospects is underlined by the potential for change; this was a roster made to be leveraged, through young talent and team-friendly salary filler, into a trade. Stevens has in-hand an impressive defense that could still be improved upon and an offense that could be made whole with additional creators. Every dimension of this team’s current play calls attention to those conspicuous vacancies, as much current limitations as they are a suggestion of possibility.