What the Hell Happened to the Milwaukee Bucks?

It's an understatement to describe this year's Bucks as a disappointment. They're more a disappointment wrapped in an enigma, shrouded in mystery, drizzled with Greek yogurt. At 18-25, they have the eighth worst record in basketball, and their -5.0 points per game differential is fourth worst in the league. A year after being the NBA's most improved team, they're on pace to win seven fewer games this season. In many ways, it's as if last year's breakthrough never happened.

In one specific way, it's almost exactly like that. The Bucks had the league's worst defense during the 2013-14 season and then, after hiring Jason Kidd as their head coach and employing a helter-skelter, high-pressure system, shot all the way up to third in the league in defensive efficiency (per Basketball-Reference's calculations) during the 2014-15 campaign. The improvement of 8.6 points per 100 possessions from one year to the next was the second greatest of any team since the 1979-80 season, when the NBA put the three-point line on the floor for the first time.

This year, the Bucks have given almost all of that back. Milwaukee's defense has allowed 7.0 more points per 100 possessions in 2015-16 than it did a year ago. Not only is that the largest drop in the league this year by almost three full points, but it also is the 14th largest out of the 1,016 team seasons that have been played since 1979-80. When you consider that the average defense is better this season than it was a year ago, Milwaukee's drop-off looks even worse. Relative to the league average, the Bucks' D has been 7.6 points worse per 100 possessions this season, the seventh largest drop relative to league average of the three-point era.

There's no other way to put this: going from the second most improved defense of the modern era to the seventh most de-proved (dis-improved?) defense is insane, and it's worth examining just how the hell it's happened.

It was extremely unusual for a team this young—Milwaukee was the fifth youngest team in the NBA last year by minutes-weighted age, and they're the second youngest team by the same measure this year—to be that good defensively, so maybe it shouldn't be all that surprising that they've taken a giant leap backward on that end of the floor this year. The first thing that comes to mind, by way of explanation, are the offseason changes Milwaukee made to its roster.

Out went Zaza Pachulia and Jared Dudley, who each brought back future second-round picks on the trade market. In came Greg Monroe on a big free-agent contract, along with Greivis Vasquez, who was acquired from the Raptors in exchange for a protected first-rounder the Bucks had received from the Clippers in the J.J. Redick trade. That's the exchange of two solid, team-oriented defenders who worked extremely well within Kidd's system for two players who are not exactly renowned for their work on the less glamorous side of the floor.

Pachulia started 45 games for the 2014-15 Bucks, including the final 26, as well as all six of their playoff games. At 30, he was the elder statesman of the team, and he was reliably in the right place at the right time; per the Nylon Calculus rim protection numbers, he also saved the Bucks 7.1 points per 36 minutes with his ability to protect the basket. Dudley reinvented himself as a small-ball power forward, showing a surprising ability to hold his ground in the post against bigger players while also seamlessly switching assignments, helping aggressively in the paint, and getting back out to his man on the perimeter. He could not have been a better fit with what Kidd wanted to accomplish with his defense.

Monroe has almost never been what anyone would term a plus defender, but he did improve last year once the Pistons excised Josh Smith from their roster. He was brought in mostly to help the Bucks on the other end of the floor—despite all their improvement last season, Milwaukee couldn't score at all, and that became an especially disastrous problem during their playoff loss to the Bulls. It was that sagging offense that likely motivated the Vasquez trade, as well, the thinking being that he'd upgrade their backup point guard slot behind Michael Carter-Williams and help out next to MCW on occasion. Vasquez, too, has long been a subpar defender.

Just swapping out two solid-but-not-great defenders from the rotation and replacing them with two below-average-but-not-atrocious ones isn't enough on its own to sink the Bucks' defense as it has been sunk this year. John Henson not being able to carve out a bigger role for himself, Carter-Williams not quite fulfilling the defensive potential his crazy-limbed body seems to promise, and the return of Jabari Parker have all contributed to the downfall in different ways and to different extents. A look at the Bucks' performance over these past three years in the Four Factors makes clear the specific areas that have been affected this season.

Shooting and turnovers, the two big areas where the Bucks improved most last season, have unsurprisingly been areas of great regression this year. Not forcing quite as many turnovers is probably the more damaging one for a team with Milwaukee's offensive struggles—given their spacing challenges, getting their athletes out on the break is even more important for the Bucks than it is for other teams. Considering that Milwaukee is one of the best transition teams in the league—they shoot 55.7 percent on the break and turn 17.7 percent of their transition opportunities into free throws, the third highest rate in the NBA, per Synergy Sports—and in the bottom third of the league in half-court points per 100 possessions (per Nylon Calculus), that lack of opportunities on the break hurt even more.

Milwaukee's shot defense has been a big bugaboo, too, largely because of the type of shots they're giving up and allowing opponents to convert at a higher rate.

The cracks that open in the Milwaukee defense this year are yielding better opportunities for opponents than they did a year ago. The Bucks haven't been forcing teams to take quite as large a share of their shots from mid-range, the least efficient area of the floor, and instead allow them to shift those shots into the paint and behind the three-point arc. It surely doesn't help that the Bucks have also allowed opponents to shoot a higher percentage in the paint, or from mid-range, or on above the break threes, as well as on shorter corner three-point shots. They've done all those things.

It's the performance in the paint and on corner threes that hurt the most, of course. It's well known by now that those are the two most efficient spots on the court, and regression in those areas accounts for almost all of the Bucks' total regression in effective field goal percentage defense.

The corner-three issue may be a random blip that reverses itself in the second half of the season: the current 43.1 percent that Milwaukee is allowing seems rather unsustainable, even for a team leaving teams open behind the arc as often as the Bucks are. The closest defender has been 6-plus feet from the shooter on 12.9 percent of opponents' three-point shots, the fourth highest rate in the league, per SportVU tracking data analyzed by NBASavant. Since no team has shown the ability to effectively suppress three-point defense on a consistent basis across a long period of time, preventing teams from taking threes at all is the most advantageous strategy. The Bucks haven't done that as well as last year, either.

Luckily for the Bucks, all of this is probably not quite as big an issue in the long-term as it is in the here and now of this season. Milwaukee is essentially in Year 1 of the Giannis-Jabari-Khris Middleton trio that forms the foundation of its roster, and that roster will likely turn over multiple times by the time those guys hit their primes four to five years from now.

The Monroe deal, which hasn't worked out as planned so far, has an opt-out (for Monroe) after next season, and the Bucks can always go in another direction if they so choose. They can probably get more in a trade for Monroe at this deadline than they would be able to at next year's, but it might be worthwhile to give this particular core group another shot once Parker, who had ACL surgery last year, gets his legs back and with Coach Kidd, who is recovering from hip surgery, on the bench for the full season (the Bucks have been coached by assistant Joe Prunty since mid-December). Milwaukee can move on from Carter-Williams, too, if they wish, although that would be painful considering how much they gave up—Brandon Knight, and passing on the protected Lakers draft pick that was redirected to Philly in the deal—to get him.

In the meantime, Milwaukee needs more of just about everything. They need more shooting—Middleton is the only plus shooter in their rotation at the moment—and more rim protection, and someone other than Giannis or Parker who can penetrate off the dribble. They need to either get back to the controlled scrambling on defense that defined their rise last year or scrap that system and find a less frantic approach that still leverages their length and athleticism into forcing opponents to take uncomfortable and inefficient looks.

It's disappointing that Milwaukee didn't find those things this year, after making a big push by signing Monroe. Still, it's not the end of the world. The Bucks are a few years away from their best players being at their best, and because of that, they have some time to work out the kinks. For all the ways in which they've gone backward, the future is still pretty bright.