When the Bulls fired Tom Thibodeau, they abandoned their devotion to being an elite defensive unit. They wanted to stay hip with the times, so they brought in an offensive minded, mild-mannered, anti-Thibs in Fred Hoiberg. Most people thought the Bulls' defense would completely crumble under Hoiberg, but some remained hopeful that the Thibodeau-forged unit would sustain the paradigm shift.
Through the month of December, the Bulls, for all their offensive struggles, remained a top-3 defense in the league. With a defensive rating of 98.2, they trailed only Boston and San Antonio. Since January 1st, it's been a different story. Ranking 16th in the league, the Bulls are allowing 104.2 points per 100 possessions.
Now, more than halfway into the season, the Bulls are eighth in defensive rating (100.3). Per NBA.com SportVU data, they force opponents into the most defended field goals (91.7). They hold opponents to the lowest field goal percentage in the league (42.5) and the fourth lowest three point percentage (32.7).
Seth Partnow of Nylon Calculus, did some really important research last year, to prove that there is no correlation between holding teams to low three-point percentages and good defense. It is luck. If you want to prevent teams from scoring, you have to take away the three-point shot altogether, not just hold teams to low percentages.
Similarly, the "defended field goal" as listed on SportVU data, is an incredibly tricky because it only signifies whether a defender was within a certain distance from the shooter, but it doesn't tell whether or not the defender altered the shot.
Here, the Bulls are actually doing really well. Allowing only 22.7 three's per 100 possessions (24.9 percent of opponent field goals, 3rd in NBA), they are one of the top-8 teams in taking away the three. They allow only 2.6 left corner threes (7th) and 2.0 right corner threes (2nd) per game. Directly from the Thibs playbook, taking away the most damaging weapon from the opponent, and forcing them into tough, mid-range shots is a sure-fire way to keep you in a game.
For reference, here's the Bulls field goals allowed, by area, compared to Thibodeau's tenure, via NBA SportVU data.
Overall, the Bulls do a good job of limiting opponents by taking away the corner threes and running them into mid-rangers. The glaring disparity, however, is the amount of shots the Bulls allow at the rim. In the world of Moreyball, defenses can't just take away the three-point line. Layups and dunks are among the highest expected points per shot, so allowing so many restricted area attempts is bad news for the Bulls.
Despite their gaudy defensive rating, the Bulls have had problems all year. They force the fewest turnovers per 100 possessions in the league (11.8), they allow the most offensive rebounds per 100 possessions (12.6) and force opponents to commit the sixth fewest fouls per 100 possessions (19.0). These are three of the most important ways to bolster an efficient offense. Taking away possessions from the opponent not only prevents them from scoring, but can often turn into easy, fastbreak offense. The Bulls rank 28th in fastbreak points per 100 possessions (9.9) and 29th in points off of turnovers (13.6). Conversely, allowing the opponent to get extra possessions (via offensive rebounds) is the reason why the Bulls allow their opponents the third most, second-chance points per 100 (14.6). Scoring after events like offensive rebounds or turnovers have a higher expected production output and can severely change the game's momentum.
Gasol: "I don’t care about missing shots. I care about defensive mistakes and breakdowns."
— K.C. Johnson (@KCJHoop) January 26, 2016
Aside from the stats, the defensive execution has been excruciating. Missed assignments run rampant. Pau Gasol has rightly taken the brunt of criticism for missed boxouts and an unwillingness to step out to contest shots.
After missing the box out, he looks around to see who he can blame for it.
Great box out https://t.co/1X6Au5P3s0
— Will Gottlieb (@wontgottlieb) December 29, 2015
He rarely steps out to contest shooters, a display of age and low effort.
Pau's effort is trash https://t.co/Y3r1edvkzY
— Will Gottlieb (@wontgottlieb) January 9, 2016
Here, Jimmy Butler gets over the screen (which signifies no switch) but Gasol stays to contain Dwyane Wade. So Wade kicks it out to Chris Bosh at the top of the key, and Butler has to cover for Gasol. Bad communication in an important, late game situation.
Jimmy just got over screen to stay on Wade AND got out to top of the key to contest Bosh. Pau just stands still https://t.co/kE794GRybQ
— Will Gottlieb (@wontgottlieb) January 26, 2016
This is the absolute quintessence of what Gasol is able to do defensively. Because he likes to give himself space to contain pick-and-rolls (which, given his age and speed, is fine) he is in a great position to block shots at the rim. But he gives no effort to go after the loose ball or contest the second chance shot.
No play will ever better reflect what Pau Gasol does and doesn't do on D https://t.co/xfvHzfPzCt
— Cody Westerlund (@CodyWesterlund) January 18, 2016
While these plays are egregious, it’s not just Gasol. This is not meant to be a Gasol bashing fest. For his lack of speed and quickness, Gasol does an okay job of containing pick-and-rolls and forcing guards to take floaters, which are tough shots to make. Gasol is an easy scapegoat but the entire team needs to improve.
Derrick Rose often gets lost on screens and switches.
Rose getting completely lost on the switch. Winslow gets a wide open layup https://t.co/CcD3oXlVBp
— Will Gottlieb (@wontgottlieb) January 26, 2016
Here, Rose loses Justise Winslow COMPLETELY. Winslow sneaks behind and waits for a pass directly under the basket for an easy two.
These are just a handful of errors, but they wreak the signs of an undisciplined team. While the Bulls might have some nice defensive numbers, they are not close to the team they were under Tom Thibodeau. That’s why really smart teams like the Atlanta Hawks and the Golden State Warriors were able to surgically dissect the Bulls in their contests.
So far, the Hoiberg regime has put on the facade of maintaining the defensive foundation on which the Thibodeau era was structured. While the transition hasn't supported the defensive integrity (they're switching more on pick-and-rollss rather than Ice-ing), the defensive rating remains solid. Frustrating as it may be, the Bulls don’t have to be perfect right now. They need to put in a lot more work to be a cohesive unit by the time the playoffs roll around because they won’t be able to flip the switch and lock teams down all of a sudden.