76ers unable to solve Celtics’ Chest series in Game 3

In the fourth quarter of their Game 3 win over the Philadelphia 76ers, the Boston Celtics found something that worked and weren’t shy about going back to it as often as possible: their Chest series generated good offense throughout the final period of regulation and the five minutes of overtime play. Brad Stevens ran everything through Jayson Tatum, who orchestrated the offense like a ten-year veteran instead of a rookie who this time last year was doing pre-draft workouts for the teams at the top of the lottery. Chest is an exceedingly simple series of set plays that can flow into quite a few different actions, though the Celtics almost exclusively went with one option: the follow pick-and-roll variation, in which the player setting the original cross screen follows into a ball screen:

Chest begins in a Horns alignment, in which the ball starts in the middle of the floor, two players are at the elbows, and two players are in opposite corners. Unlike a majority of Horns-based offense, Boston has some of the traditional roles switched: usually, the point guard brings the ball up, both big men are at the elbows, and the wings occupy the corners. In Boston’s Chest series, Tatum exchanges roles with Baynes, who spaces out to the corner.

To trigger the Chest series, Marcus Morris steps across and sets a cross screen for Tatum to exit from the right elbow to the left slot, where he receives the ball from Marcus Smart. Smart then spaces out to the right wing, Morris follows Tatum to the left slot to set a ball screen, and Boston plays the pick-and-roll or pick-and-pop from there.

The spacing on the play is incredibly important, especially when Morris (or Al Horford, when he was inserted as the screener) pops to the three-point line after setting the ball screen for Tatum. Because there’s only one player in the weak-side corner, it’s very difficult for the defense to cover both Tatum and the big man who pops to the wing. Coach Daniel released a great video explaining the finer points of the Celtics’ pick-and-pop scheme and how the 76ers have reacted to it; I highly recommend watching it to get a better understanding of how Boston’s spacing works on these plays. In the above clip, Dario Saric is slow to help off Morris, leading to an open lane to the basket for Tatum. T.J. McConnell, who is guarding Terry Rozier in the left corner, is of no real use as a help defender because that rotation up to Morris would be too long and would leave an even better three-point shooter open in the short corner.

The next time down the floor, Joel Embiid helps down into the paint to deter Tatum’s drive, which leaves Baynes open on the cut. Had he caught the ball cleanly, Baynes had a dunk, but even without that, the Celtics got a good look from Morris on the perimeter:

The 76ers kept their defensive assignments the same, so the Celtics went back to the well time and again for the next few minutes. Philadelphia changed up their coverage of the Tatum-Morris screens, which at least made it more difficult for Tatum to get in the lane and score, though he was able to do so anyway:

This is better from Philadelphia—Marco Belinelli and Saric switch the original cross screen, then switch back when Morris follows to set the ball screen for Tatum. Morris rolls this time, then exits to the left corner, while Rozier lifts up to the left wing to replace Tatum. Boston generates no real advantage in the Chest action, but Tatum is able to overpower Belinelli to get to the rim and score on the putback anyway.

Following a few substitutions for both teams, Philadelphia removed Belinelli from his position guarding Tatum for the next possession, switching Redick to Tatum and bringing in Ben Simmons to defend Smart. Redick and Saric trap Tatum on the ball screen in order to force the ball out of Tatum’s hands, but this leaves Morris open on the roll. Belinelli is the man guarding Jaylen Brown in the weak-side corner, meaning it’s his job to rotate and cover Morris, but he doesn’t get there and gives up the layup at the rim. Belinelli is not entirely to blame for the defensive breakdown; Tatum breaks the Redick-Saric trap by getting around Saric and essentially turning the play into a 5-on-3.

The next trip down the floor, Tatum rejected the cross screen and exited to the right wing, where he went right past Robert Covington as if he were Marco Belinelli:

Covington’s defense has been worrying throughout these playoffs; he hasn’t been nearly the lockdown perimeter defender he was during the regular season. Tatum’s had no trouble getting to the rim against him and he’s been caught out of position helping into the lane a bit too much, though his ability to dig into ball handlers and still recover to the perimeter is a big part of his defensive value. Covington’s had his fair share of issues guarding Tatum; per NBA.com’s matchup data, he’s defended Tatum for 77 possessions, on which Tatum has shot 11-for-20 from the field and drawn one foul. Additionally, Boston’s scored 94 points on these 77 possessions for an astronomical 122 offensive rating.

After about six minutes off, the Celtics returned to Tatum to close the fourth quarter and overtime, running Chest five more times in the final two minutes of regulation and overtime. Against Simmons, Tatum rejected Horford’s cross screen and hit the midrange jumper:

Philadelphia switched Belinelli back to Tatum on the next possession, so Tatum attacked him again, though this time Belinelli didn’t give up on the play in pick-and-roll defense and actually forced Tatum to give the ball up to Horford, who missed the three-pointer in the late-clock pick-and-pop:

In overtime, Belinelli continued with his Tatum assignment, but the 76ers got even more aggressive with the trap, using both Belinelli and Ersan Ilyasova to trap Tatum as soon as he caught the ball off Horford’s cross screen:

The trap worked—Tatum had to give up the ball—but the rotations caused by the high trap left the 76ers vulnerable and Morris was able to drive past a closing Embiid and find Horford in the paint for an easy layup.

Searching for answers, Philadelphia switched up the matchups again, this time putting Saric in the game to guard Morris and moving Embiid to Horford, bringing him directly into the Chest action. Tatum circles around Horford and draws both Embiid and Belinelli to him, though this time Belinelli drops off to switch onto Horford:

Finally, the 76ers go back to their original plan of letting Belinelli fight through the screens and dropping their big man into the paint to deter any drives to the rim, which didn’t work in the least:

No matter what Philadelphia tried against Boston’s Chest series, Tatum or one of the other Celtics was able to wreak havoc on their defense and leave them constantly changing up their coverage, hoping to find something that worked. Nothing did, and the Celtics were able to take Game 3 and a commanding 3-0 edge in the series.