Even in the darkest days of last season, the Chicago Bulls always could count on their defense.

The offense was shaky at best. Star players such as Zach LaVine struggled to find their footing. But the Bulls could put the clamps on nearly every opponent, finishing fifth in the league in defense in a 40-42 season.

That last modicum of consistency has vanished for the Bulls, who have transformed into a bottom-10 defense — a slow-moving, disjointed, skittish shadow of its former self. Losses such as Sunday’s 118-109 defeat against the Brooklyn Nets punctuate the Bulls’ inability to squash opponents when they get on a scoring run.

As opponents continue to carve up the defense, coach Billy Donovan has a simple goal for the Bulls: get in the way.

“We have got to put our body in plays,” Donovan said. “There’s no getting around it. We’ve got to, as much as we can, take some more charges. We may not have the verticality to go up and contest all the time in certain positions, but we can be there early to have a body in front of players coming downhill.”

The defensive drop-off is one of the most baffling aspects of this Bulls season. The Bulls weren’t immediately stellar on defense last season. At this point they had the ninth-best defensive rating in the league (110.5), and that dropped as low as 20th in January before the Bulls began their ascent back to a formidable defense.

Sure, it took time for the defense to click last season as players learned one another and melded into a set style. But the majority of those players returned this season. And the only two additions — veterans Torrey Craig and Jevon Carter — were purposefully selected for their adaptability and defensive versatility.

So why is the defense off to such a slow start?

“A lot of it is communication,” center Nikola Vučević said. “We don’t do a good enough job communicating to each other what we have to do or honoring the call if somebody calls. Even it’s wrong, we’ve got to honor whatever that person feels like is the right call.”

While communication and slow rotations are bigger-picture issues to address, Donovan said the Bulls also need to clean up two key areas: rebounding and transition defense.

The Bulls are the second-worst defensive rebounding team in the league (30.1 per game) and allow 10.9 offensive rebounds per game (15th in the league). As a result, they give up 14.9 second-chance points per game — in the bottom 10. This is a drastic switch from last season, when the Bulls gave up the second-fewest second-chance points (11.9 per game).

But Donovan’s analysis doesn’t entirely translate to transition defense. The Bulls give up only 11.8 fast-break points per game, the fourth-fewest in the league — and a slight improvement from last season, when they allowed 12.8 per game (seventh-fewest).

Statistically, the defensive quandary for the Bulls is curious. They’re a top-five team in key areas — opponent points off turnovers (14.3, second), opponent points in the paint (42.2, second) — and average 8.2 steals, seventh in the league.

It’s clear, however, that the main problem lies in one area: defending teams in their half-court sets.

Take Sunday’s loss in Brooklyn, where the Nets made 25 shots from 3-point range — the most allowed in a single game in Bulls franchise history. Some of that was the result of a hot-handed night. But on many rotations, the Bulls simply gave up on close-outs or stopped moving through their rotation, leaving 3-point shooters wide open in the corners.

This comes back to the same source: Poor communication creates poor defense.

“(We’ve) just got to do a better job being on the same page, communicating whatever the coverages are and getting there,” Vučević said. “It’s tough when you let the ball get downhill and the initial coverage breaks down and you’re in scramble mode. With so much space and so much shooting around the league nowadays, it’s hard to make up for all that space.”

It’s clear this has been somewhat broken since the opener. And it only gets worse when the Bulls don’t have Alex Caruso, who is universally acknowledged as the best defender and loudest communicator on the roster.

There’s still time to course correct — after all, it took three months for the Bulls to lock into their best defensive form last season. But if they don’t commit to what used to be the strongest part of their game, the outlook for this season will remain trapped in this losing cycle.

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