The evolution of the Celtics offense is ready for this rematch with the Wariors

Derrick White took a trip from above the break into the paint and across the baseline to the corner, shaking Nic Claxton as the Nets stacked the paint with bodies against Jayson Tatum. Tatum dribbled forward and tossed a pass to White, who hit a three, as Boston managed 109 points on 47.7% shooting to beat a budding Brooklyn defense.

The Nets shared the personnel and scheme to bother the Celtics in ways the Warriors did in the NBA Finals. Show two bodies in the paint. Take the rim away. Limit how much Tatum and Jaylen Brown can collapse the defense and find kick-out passes. Brooklyn switched everything and Ben Simmons and Claxton’s presence in the paint bothered Tatum, who shot 7-for-22.

“(We) just make the right play,” Marcus Smart told CelticsBlog/CLNS Media in Brooklyn. “You’ve got to have a rim threat, and then you just find the open guys if (teams double team). We have the advantage if J.T.’s driving and he has a defender on him, and they bring an extra defender. That means somebody’s open and we just got to find him.”

“Once we do that, and ironically, the ball finds J.T. again, and he’s the one who passed it, the team’s in scramble mode. They’re trying to stop every threat that they see and they forget about J.T. That’s just how we’ve got to play. When we play that way, it’s tough to beat us.”

Teams that can throw multiple bodies at Tatum in the paint fare better against the Celtics than those, like the Hornets, who tried doubling him at the point of attack. Charlotte allowed Tatum to make easy passes to Derrick White, Grant Williams and others in the short roll, who beat the Hornets’ back-end rotations. Without rim protection, Tatum powered to 7-for-10 shooting in the paint during his 51-point performance on Sunday.

A more active Tatum found different ways to reach the rim in the first half of the season too, whether as a roller (1.8 possessions per game), cutter and his transition runs rank in the 79th percentile of the league in terms of points per possession.

Offense starts with defense for a team reforming its identity around its double-big lineup, and Al Horford and Robert Williams, who both missed the Celtics’ loss at Golden State in December, own a 99 defensive rating together. When they play with Tatum, they boast a 118.6 offensive rating. Joe Mazzulla recently lauded Boston’s 1.34 expected points per possession when Horford and Williams pair.

Their absence didn’t totally explain Boston’s stagnancy in the last Warriors game though. Blake Griffin played active minutes in a spot start. Grant Williams played strangely passive out of the corner. The Warriors neutralized shooters like him by switching, as they did in the Finals, and Boston shot 30% from three. While it didn’t all fall on Tatum, he shot 6-for-21, struggled to shake Klay Thompson and Jonathan Kuminga, and his off-ball movement waned.

“Against great teams, whether they’re switching, whether they’re showing, whether they’re maintaining, you have to be able to go to different packages, and you have to be able to coverage solutions,” Mazzulla said at practice Wednesday.

Mazzulla explained the Celtics switched their play calls and their frequency several times during their recent win over Brooklyn. Boston doesn’t call plays from the sideline, instead empowering their plays to make reads from a base package of plays, whether built around the side, middle, or off-ball actions. The Celtics aim to create advantages, and Mazzulla saw them at their most stagnant playing five-on-five, failing to set a proper screen, or making wrong reads.

The team involved Robert Williams more in the high post in the Charlotte mini-series, sending their wings and guards downhill in those mismatches. Transition always creates opportunities for finding cross matches, though Boston’s half court execution ultimately set the team apart as a historic unit early this year. Shades of that execution has returned recently.

“Continue to move, create space, move without the ball, set screens,” Tatum told CelticsBlog/CLNS. “If I had an ISO, they were sending an extra, blitzing the ball screen. Just things that we are aware of going into games and just make the right read, draw two, drag them up, find the open man, play four-on-three, pass up a good shot for a great shot.”

Tatum’s isolation possessions each game (4.1) fell below his average each of the last two years (4.7). His activity away from the ball changed everything for Boston’s stagnant offense from the Finals. Thanks to that, he no longer ranks among the top-20 players in double teams received each night, according to NBA’s CourtOptix data.

The Warriors don’t want to double him though. They feel comfortable drawing him into mismatches, loading up at the rim at the last second and funneling the ball back to players like White and Smart.

The key for Boston tonight involves relocating Tatum in new spots on the floor through secondary drives or actions, instead of firing up the threes Golden State gives Boston’s role players.

Mazzulla emphasizes the need to fight for proper spacing. That provides access to the rim, allowing both Brown and Tatum to shoot 70% inside this season, better than elite finishers like Zion Williamson, Shai Gilgeous-Alexander and Domantas Sabonis. That’ll be necessary to beat the Warriors.

Those actions stem from free-flowing creativity they practice, rather than set plays. That disappeared in December and returned in encouraging ways against a Brooklyn defense that mirrored the Warriors’.

“J.T. gets a lot of attention. They try to make it as difficult as they can and crowd it for him,” White told CelticsBlog/CLNS in Brooklyn. ”It’s on other guys to stay spaced, cut, be in the corners, be in the right positions and just be ready to make the play after that. Obviously, there were some possessions where we didn’t have great spacing, and the opposite is when we did the right things and got great looks.”