What’s wrong with the Nets defense and how can they fix it?

It was a given when the Nets traded away Kevin Durant and Kyrie Irving that their offense would take a step back.

But shockingly, it’s been the defense that’s taken two or three steps back — and stumbled off a cliff.

“We were all concerned about us scoring and putting up points — and I think we have enough firepower to do that — but we have to take our defensive mindset to a different level,” Jacque Vaughn said. “We have to be extremely confident in guarding the guy in front of you and take pride in doing that because that’s the first part of our defense.”

Even after Friday night’s stirring come-from-behind victory in Boston, the Nets have just a 2-6 record since officially moving on from Durant and Irving (they are 3-8 since they agreed to trade Irving). And despite bringing back accomplished defenders in 2022 Defensive Player of the Year runner-up Mikal Bridges, Dorian Finney-Smith and Cam Johnson, it’s that end of the floor that has been the biggest disaster.

On Feb. 11, the Nets were 33-22. They were 12th in the NBA in defensive rating (112.9) and eighth in net rating (2.4). With their star-studded offense, it had been just enough to make them a contender.

CJ McCollum drives against Kevin Durant, Nic Claxton and Kyrie Irving
With Kevin Durant (7), the Nets were title contenders with a top-12 defense.

But they own the third-worst defensive rating (121.3) and second-worst net rating (-11.5) in the league since that date — and that includes limiting the top-three Celtics offense to just 68 points over the final three quarters on Friday night.

“You can see them trying to learn on the fly,” one Eastern Conference scout told The Post.

Switching from switching?

It all begs the question: Why did the Nets defense collapse?

And how do they fix it?

The Nets switch more often and more extensively than any team in the league. That’s been part of their defensive DNA for years.

Jacque Vaughn coaches the Brooklyn Nets
Jacque Vaughn is tasked with rebuilding the Nets defense around four new starters.
Noah K. Murray for the NY Post

The Nets used to be a more conservative drop coverage team under Kenny Atkinson with DeAndre Jordan and Jarrett Allen at center. But when Vaughn took over as the interim coach in early 2020, he sprinkled in elements of switching, and the Nets continued that scheme when Vaughn was Steve Nash’s lead assistant for two-plus seasons.

Once Nic Claxton supplanted Andre Drummond at center, the changeover was complete. The Nets leaned all the way into switching, doing it one-through-five. Vaughn replacing Nash on Nov. 1 just cemented that.

The Nets moving away from switching on defense is like Jason Kidd’s fast-break Finals teams bleeding the clock in the four corners or the organization suddenly being transparent about injuries.

But in Wednesday’s 141-118 humbling at the hands of the Knicks, the Nets tried deploying drop coverage.

It’s off-brand. But desperate times…

Jalen Brunson puts up a shot as the Knicks beat the Nets.
Knicks point guard Jalen Brunson torched the Nets defense to a record-setting extent in the rivalry game on March 1.
Getty Images

The Nets coughed up 81 first-half points — the most in team history — as the Knicks shot 68.1 percent from the field and 14-of-20 from 3-point range. Jalen Brunson lit them up for 30 points by halftime. The Nets switched to blitzing in the second half, which at least limited Brunson to nine points the rest of the way.

“We tried some different things schematically [Wednesday] to get a look at it, and there was some positives and some negatives about it,” Vaughn said. “We just haven’t had time to practice that. We’ll use some opportunities going forward to practice different schemes, because we’ll need it going forward.

“I’m learning the strengths and weaknesses of this group, not what their previous stops were. It’s the culmination of this group together and what it presents. So I’m learning that, and my job is to convince them to buy into us doing it together.”

The experimentation likely will continue following the reported signing of rim-protecting center Nerlens Noel, whose contract was bought out by the Pistons.

“For the last few years what I’ve been doing here, one-through-five everybody is switching, even with the center,” Cam Thomas said. “[Wednesday] we tried to do it one-through-four, and with the center dropping, but … we’re just trying to find the right formula.

“There’s so much we’re trying to figure out quickly, because the playoffs are right around the corner and we still want to be in the playoffs, so we just have to hurry up and find a formula that works for us. But that’s going to take some time and everybody is new, and we need some time to work with each other.”

Quentin Grimes drives past Spencer Dinwiddie.
“We’ve got to kind of hone in on which defense we’re going to play,” Spencer Dinwiddie (26) said of the Nets’ experiments with an adapted scheme.

With just 19 games left on the slate, time is a luxury the Nets don’t have.

“Obviously we’ve got to kind of hone in on which defense we’re going to play,” Spencer Dinwiddie said, “and then from there just try to execute it at the highest level possible.

“We’ve got to get on the same page.”

The ins and outs of ‘red’

Slowing down that process is the fact that four of the Nets’ five starters recently arrived from teams that played significantly different defensive schemes: Bridges and Johnson in Phoenix, and Finney-Smith and Dinwiddie in Dallas.

That’s not shocking: Brooklyn’s style is more outlier than the norm. But it’s making the learning curve steep.

Gregg Popovich coaches up Jacque Vaughn during a Spurs game in 2007.
The Nets’ system of guarding the post with baseline traps is adapted from Gregg Popovich, Jacque Vaughn’s former coach with the Spurs.
NBAE via Getty Images

“It’s been a challenge for everybody,” Claxton said. “Mikal, Cam, because they’ve been defending one way the past few years of their career. And now we’re trying to find a middle ground. Now I’m having to defend ways that I haven’t really guarded since my rookie year.”

To compensate for opponents trying to punish their lack of size, the Nets have relied on “red” tactics.

In layman’s terms, it’s when they front the low post and have a second defender come over from the weak side to double-team. The Nets deploy plenty of traps on the baseline to try to negate their size disadvantage.

For years, Gregg Popovich’s powerhouse Spurs teams were the best in the league at “redding.” Vaughn spent six seasons in San Antonio as a player, scout and assistant coach. (Steve Kerr’s Warriors later adopted and adapted the Spurs’ scheme to overcome their lack of size and maximize Draymond Green.)

The Nets’ principles are a far cry from the Suns’ old-school drop coverage with center Deandre Ayton patrolling the paint. And when they did red, it was off the ball.

Kristaps Porzingis attempts a layup against the defense of Mikal Bridges and Deandre Ayton.
Mikal Bridges (left) was steeped in different defensive coverages during his days with the Suns and center Deandre Ayton (right).

“That’s always tough, just being somewhere and the principles are just pretty much different,” Bridges said. “Just [switching] one-through-five, ‘redding.’ Usually [the Suns] played ball-screen defense like in a drop or in a ‘mush’ or something like that.

“…It’s a little different knowing how to navigate screens into being up and being ready to switch when the big sets it, and then being low man, being in that dunker [spot] sometimes on the block. That’s not many times I’ve been in that position, but it’s just learning and just knowing what to do.”

’A new kind of mindset’

For this remade Nets roster, it’s been like learning a new language — and knowing how to speak it in unison at full speed with games on the line.

“It’s not just learning new terminology,” said Bucks coach Mike Budenholzer, who tutored Atkinson. “It’s learning new techniques and skills, a new kind of mindset.”

Mike Budenholzer draws up a play in the Bucks huddle.
Mike Budenholzer, who coached the Bucks through a defensive scheme change, warns that it takes time to implement.

Budenholzer’s Bucks went from being a drop team to trying to switch on defense to finally learning how to do both to get past the Nets in the 2021 postseason en route to the title.

“If it’s your first time changing and [new] concepts, teachings, and technique and mindset — it’s going to take [time],” Budenholzer said. “There’s going to be an adjustment period. There’s going to be a growth time. So it’s not easy for guys to do that.”

The results show it’s not easy. But for better or worse, that’s the job.

“Bottom line is we’ve just got to be better,” Johnson said. “We’ve got to find a way and learn how to make teams do things that they don’t want to do. It’s one of the key things to defense in this league, because the reality of it is: In the NBA, guys are really good, and they can score. You let them get to their spots, they’re going to score all day. You let them shoot the shots they want, and they’ll score all day.

“[We have to] continue to chip away and learn and grow and use these as lessons. Sometimes you just go through things headfirst, live with these results, and go back to the drawing board and be better from it.”