How Celtics shut off the Mavericks’ offense in Game 1 of 2024 NBA Finals

There are certain buzzwords in the NBA that form immediate associations between them and certain players, teams, and coaches. Hearing the phrase “Triangle Offense” makes one think of Phil Jackson and his championship-laden tenures with the Chicago Bulls and Los Angeles Lakers. “Seven Seconds or Less” has been credited to Mike D’Antoni’s Phoenix Suns of the mid-2000s, a pioneer of the pace-and-space era that has become ubiquitous. A slightly lesser known — but arguably equally influential — concept: the “Corner Offense,” championed by Rick Adelman and his early 2000s Sacramento Kings squad.

Central to both the Triangle and Corner offenses is the split action — a concept that captures the zeitgeist of the Golden State Warriors’ dynasty, who have both Jackson and Adelman to thank for being progenitors of their vaunted motion offense. While the split action is still associated with the Warriors, it has become a much more common action in the NBA.

Part of the reason why most observers probably won’t be able to detect a common split action nowadays is due to a simple difference in location. When one hears of a split cut, it would most likely be of the low post variety made popular by the Warriors, who sliced and diced opponents with the action with help from the otherworldly talents of Steph Curry.

The split action setup below is probably what most people would visualize:

While Jackson’s Triangle principles also required the post playmaker to be occupying the low block — similar to Steve Kerr’s interpretation of the split action above — Adelman’s corner offense had the big-man hub up higher at the elbow, also known as the high post. In that regard, the early-2000s Kings had what one could call a “high-post” split — locationally opposite to Kerr’s version, but conceptually similar in philosophy.

What is the overarching philosophy of the split action? The result can vary depending on how the defense reacts — but the first goal is to almost always create space for a shooter around the split-cut screen. If the defense opts to switch the action, two mismatches are created: one where a quicker perimeter operator has a bigger and slower man on him, and one where a burlier player has a smaller defender guarding him. Slip opportunities can also be created from split cuts, either as a counter to switching or a response against “top-locking” (denying an off-ball player from using a screen by jumping in between the player and the screen).

While not particularly known for heavy usage of the split action, the Boston Celtics do make use of it to induce a reaction from the defense — and hopefully produce a result that ends up in one of the aforementioned outcomes. Like the Adelman version (and, by extension, the Denver Nuggets’ version), the Celtics prefer to run their split cuts through the high post.

Unlike the Adelman version, where the split cuts happen on the ball side, the Celtics’ split cut happens on the opposite side:

There is a deeper intention within Jayson Tatum’s attempt to set a screen for Derrick White. Bypassing the traditional method of hunting for a mismatch, having Tatum start off the ball and set a screen for whoever Kyrie Irving is guarding is a somewhat unorthodox approach to coax a favorable matchup — yet, like the split action, it is building up quite the support base in NBA circles and is quickly becoming a conventional tactic; more and more teams are having their perimeter creators set off-ball screens in this manner.

In the case above, Derrick Jones Jr. and Irving manage to stay home, with White quickly relocating to the dunker spot, forcing Irving to follow him. Almost simultaneously, Jrue Holiday fakes a handoff and keeps the ball on a sudden drive — which places Irving in a precarious position to have to help off of White on Holiday’s drive. Holiday sees the crease and dumps the ball to White for the easy layup.

The Dallas Mavericks’ version is nearly identical to that of the Celtics’ — but the key difference lay in how the Celtics defended the action:

Perhaps knowing that Holiday and Tatum would simply switch the split cut, Irving tries to get the jump on Holiday by rejecting the screen and coming off of the handoff by Jones. What Irving doesn’t expect is how fast Holiday is to recover, navigate over the screen, and keep Irving wary of his presence behind him, which discourages Irving from pulling up. With Al Horford as Holiday’s partner in pick-and-roll defense, there’s an additional sense of comfort and security — both of which Horford justify by corralling Irving’s drive and forcing the miss.

More important to note are White in the weak-side corner (the “low” man) and Jaylen Brown on the ball-side or strong-side corner:

Because of how effective Horford is at containing Irving’s drive, Brown isn’t compelled to help off the strong-side corner, nor is White tempted to step inside the paint, lest a skip opportunity to PJ Washington is created. The trust in Horford to take care of the action up front eliminates the need for rotation — which is the crux of the Celtics’ defensive approach to this series.

It may be reductive to attribute a micro-battle to the fate of an entire contest, but this series may come down to whoever wins the war of the corners. Hidden beneath the enticing narratives this series presents is a clash between the most prolific corner-three team in the Mavericks (11.3 corner-three attempts per game, 12% corner-three rate in the regular season — both leading the league) and a defense that was among the best at limiting corner threes (7.7 corner-three attempts allowed per game, third in the regular season; 8.1% opponent corner-three rate, fourth in the regular season).

In that regard, the Celtics’ approach to getting their team victory is allowing Dončić and Irving to get their personal victories — but not without resistance, of course. If Dončić manages to reach the 30-point threshold (which he did), the Celtics wouldn’t have any problem with it, as long as he was made to toil for them (26 shot attempts). If Irving manages to support him with a 20-25 point performance (which he didn’t), it wouldn’t be the end of the world.

Which brings us to this noteworthy statistical nugget: Dončić (30) and Irving (12) combined for 42 of the Mavericks’ 89 points, while the rest of their playoff rotation accounted for 47 points. The team managed a paltry nine assists on 35 made field goals; Dončić had only one assist, while Irving had two.

With the Celtics’ stubborn refusal to help off of the corners being the culprit of the Mavericks’ predicament above, a seemingly paradoxical approach is brought to light: The Celtics are more than willing to let Dončić and Irving dominate possessions and try to score, in lieu of them finding their teammates in the most efficient scoring situations; at the same time, the Celtics are also more than willing to let those who aren’t Dončić and Irving do the scoring, as long as it isn’t from a position of efficiency.

The Celtics approached the former through two main coverages:

1. With Al Horford on the floor, they were more keen to switch everything to keep the Mavericks’ half-court actions flat. This allowed defenders to stay home on their assignments, including the corners. The trust in Horford and other “lesser” defenders to hold their own in isolation against Dončić and Irving was largely justified.
2. With Kristaps Porziņģis on the floor, the Celtics opted to put him in drop coverage in pick-and-roll situations. This kept half-court possessions a two-on-two endeavor and eliminated the need for the other three defenders to rotate, all while trusting Holiday or White to navigate around ball screens. Otherwise, they would switch screening actions that didn’t involve Porziņģis (i.e., switching 1-4).

The Celtics approached the latter by simply having Porziņģis guard the least threatening offensive player at a given moment and funneling the ball to him above the break. In the instance below, it was Josh Green who was left open and forced to create offense all on his own:

If rotations were to be forced off the corners, it would only be as a last resort. But not without switching everything beforehand, limiting options, and — as Brown is prepared to do below should Irving choose to kick the ball out — make use of a “peel” switch toward the corner to plug the hole created by strong-side help.

But upon beating Brown backdoor, Irving tries to score against the rotating Horford, who once again forces the tough shot and miss:

By limiting the Mavericks to a playoff-low 96.7 points per 100 possessions in Game 1 — 77.1 points per 100 possessions in the half court — the Celtics’ approach paid massive dividends. While taking risks through the lens of coverage conservatism seems rather paradoxical, it was a sound decision to commit all their resources toward the two heads of the dragon — and make a calculated gamble that the rest would be mere bit players instead of biting them where it hurts the most.