One Play: The Miami Heat's zone defence has the Boston Celtics at a loss

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Welcome to "One Play!" Throughout the 2019-20 NBA season, our NBA.com Staff will break down certain possessions from certain games and peel back the curtains to reveal its bigger meaning.

Today, the Miami Heat's zone defence takes the spotlight.

Context: The Heat did it again.

In Game 1 of the Eastern Conference Finals, the Heat crawled their way back from a 14-point deficit to defeat the Boston Celtics in overtime. In Game 2, they crawled their way back from a 17-point deficit to win in regulation, taking a 2-0 series lead in the process.

The Heat's offence was firing on all cylinders in their second half comeback in Game 2, exploding for 37 points in the third quarter, followed by 22 points in the fourth quarter, but it was their defence that turned the game on its head. The Celtics went from shooting 58.1 percent from the field and 42.9 percent from 3-point range in the first half to 37.9 percent from the field and 28.6 percent from 3-point range in the second half.

What changed? Miami went to a zone defence for most of the second half, which has proven to be Boston's Achilles heel in these playoffs.

Let's take a closer look at one particular possession from Game 2 to get a sense of why the Heat's zone defence was so effective.

The play: Kemba Walker commits a turnover.

Breakdown: Walker brings the ball up the court following a dunk from Bam Adebayo.

The Heat settle into a 2-3 zone on defence, with Jimmy Butler and Jae Crowder at the top of the zone and Adebayo, Duncan Robinson and Goran Dragic at the bottom of it.

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Walker begins the possession by passing the ball to Jayson Tatum on the right wing and then clearing out to the weakside. 

Crowder slides over to cover Tatum while Butler stays close to Marcus Smart, Robinson stays close to Jaylen Brown and Adebayo stays close to Daniel Theis.

The only player not "guarding" someone? Goran Dragic ... although that's about to change.

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Here's where the collective IQ of the Heat comes into play.

You see Crowder pointing after Tatum passes the ball to Smart at the top of the perimeter?

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He knows one of Walker or Brown is going to curl to the left wing. To avoid a breakdown, Crowder basically shoves Butler off of Smart to get him to switch onto Walker.

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You can see why here:

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Had Crowder not switched onto Smart, he and Dragic would've been left guarding one player (Brown) on the weakside. That would've left Butler, Robinson and Adebayo having to cover four players in Smart, Walker, Tatum and Theis.

More than likely, Robinson would've picked up Walker, which would've put Adebayo between a rock and a hard place, as he would've had to choose between following Tatum out to the corner or staying in the paint to prevent Theis from being left alone. Either way, it may have led to a high percentage shot for the Celtics.

But, of course, none of that happened because Crowder was a step ahead of the Celtics.

The result? Miami's 2-3 zone is intact.

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The Celtics actually do a good job the rest of the possession of moving the ball, but the Heat do an equally good job of rotating.

First, Crowder funnels Smart in Dragic's help, forcing him to pick up his dribble.

Then, Butler runs Walker off the 3-point line, leading to the turnover.

Why it matters: A couple of reasons.

First and foremost, this Heat team is proving to be a monster defensively. They ranked 12th in defensive efficiency during the regular season in giving up 109.3 points per 100 possessions, but it always felt as though that figure sold them short. Sure enough, they've been playing to their potential in these playoffs, ranking fourth in defensive efficiency in giving up only 106.5 points per 100 possessions.

That's after they've played five games against Milwaukee Bucks, plus two games against the Celtics, a pair of teams that ranked in the top-10 in offensive efficiency this season. With players like Butler, Crowder, Adebayo and Andre Iguodala, the Heat have proven to have the personnel to defend almost anyone and execute just about any scheme.

It helps, of course, that the Heat also have a genius pulling the strings in Erik Spoelstra, who has long been one of the league's best coaches. Spoelstra has proven time and time again in his career that he knows how to get the most out of his players and that he's not afraid to mix things up.

The 2-3 zone the Heat leaned on in Game 2? It isn't exactly traditional. Most teams have their two guards at the top of the zone and their forwards and wings at the back. In having Butler and Crowder at the top, it gives the Heat more length to throw at Walker and Smart. It makes the lives of Robinson and Dragic much easier as well because their jobs are basically to show on the wings to give Butler and Crowder time to recover and funnel anyone who gets the ball in the corner towards Adebayo's help underneath the rim.

Secondly, the zone has not been kind to the Celtics in these playoffs.

The Celtics had some success against the Heat's zone in Game 1, but Game 2 was a different story. According to Gibson Pyper of Half Court Hoops, the Celtics averaged 0.66 points per possession against Miami's zone in Game 2, which is ... not good.

This isn't exactly new for the Celtics either. Per Pyper, Synergy Sports had the Celtics ranked 27th in zone offence with 0.88 points per possession during the regular season. They've been even worse in these playoffs, scoring at a rate of 0.79 points per possession based on Pyper's tracking.

It's pretty stunning when you compare those numbers to how they've performed against man-to-man defence, both in the regular season and playoffs:

The good news for the Celtics? They know Game 2 won't be the last they'll see the Heat's zone defence in this series, giving them plenty to prepare for heading into Game 3.

The bad news? They're running out of time to find an answer to a question that's plagued them all season long.

The views on this page do not necessarily reflect the views of the NBA or its clubs.

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Scott Rafferty is a Senior NBA Editor for The Sporting News