Bulls Defensive Numbers Don't Necessarily Match the Eye Test

Bulls Defensive Numbers Don't Necessarily Match the Eye Test

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.

On Paper

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.

Screen Shot 2016-01-27 at 9.00.55 AM

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.

In Practice

 

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.

 

He rarely steps out to contest shooters, a display of age and low effort.

 

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.

 

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.

 

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.

 

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.

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  • That's why we have advanced stats, because everyone's eyes are influenced by what they already think in their own mind.

    The Bulls' Def Rtg was 101.5 last season under Thibs, 11th in the league.

    The Bulls' Def Rtg is 100.3 this season, 8th in the league.

    Posting a few vidoes doesn't change simple facts, just like I could find a few videos of the Bulls' offense running beautifully... it wouldn't change the fact that our offense hasn't been efficient at all so far this season.

    It also doesn't change the simple fact that the Bulls' defense has been more efficient this season when Gasol is on the floor vs when he isn't.

  • In reply to Bullsville:

    Thats actually the exact reason I wrote this. Advanced stats are a tool - not the be all, end all. Just because the efficiency has improved since last season (down however from '13-'14 (97.8), '11-'12 (95.3) '10-'11 (97.4) and equal to '12-'13) does NOT mean the defense is as good. The point was to explain that the defense is clearly allowing more shots at the rim, communication problems and breakdowns on PnR coverage that weren't as much of a problem before Gasol came along.

    This article doesn't address the offense being lackluster compared to expectations or the times that it has been fluid. It's about the defensive miscues that have plagued them all season. Obviously there are times where the defense looks good. Same with the offense. The point here was to explain - as the title indicates - that the numbers don't NECESSARILY match the eye test.

  • In reply to Will Gottlieb:

    The problem is, you use a whole bunch of advanced stats to try and disprove the most important advanced stat - the actual number of points allowed per possession.

    THAT'S what really matters... there are different ways of getting there, but the goal is to allow the fewest points per possession possible.

    For example, this year's team is allowing 3 more shots in the restricted area per game vs last year, but the defense is allowing fewer points per possession overall. Maybe they're challenging a lot more shots in the restricted area? Maybe they're blocking more shots in the restricted area?

    We all know Gasol is one of the top shot-blockers in the league, maybe he's also challenging and changing a lot of those shots in the restricted area?

    Whatever the reason, allowing more shots in the restricted area vs last season obviously hasn't hurt the overall defense vs last season.

  • In reply to Bullsville:

    huh? what you wrote here makes no sense and is self contradictory. Seems like you're digging deep for a way to discredit the author's overall argument.

  • In reply to Will Gottlieb:

    Also, last year was by far the worst year under Thibs, which just happened to coincide with the arrival of Gulliver, so comparing this season to last already incorporates the problems caused simply by the presence of Gasol. It would be better to compare this year(and last year) to the first 4 Thibs seasons all of which included a full dose of boozer a total defensive liability.

  • In reply to BigWay:

    Wait... so you're saying a more relevant analysis would be to compare years with even less cross over? With fewer players the same?

  • In reply to BigWay:

    Forget the advanced stats, and forget the comparison to the Thibs era... this year's Bulls team leads the NBA in opponent's FG%.

    You don't do that with smoke and mirrors, you do that by playing damned good defense consistently.

    If someone's eye test says the Bulls defense hasn't been as good as advertised, they should probably get glasses.

    I see a team that only allows their opponents to shoot 42.4% from the field and 32.8% from behind the arc (4th in the league).

    I see a team that plays outstanding defense without fouling (21.4 FTA/game, 7th in the league).

    They don't force turnovers, which is a carryover from the Thibs era. In his 5 years, they were 14, 27, 23, 17, and t-last in forcing turnovers. I'd say it's because they play sound positional defense and don't take many chances at forcing turnovers (because when you don't get the steal, you wind up out of position, which compromises the team defense).

  • Will, another great analysis. Keep it up! I think most of us knew that this team wasn't as good defensively as some stats indicated, but you've added clarity to that hunch.

  • In reply to Roman F:

    I appreciate that Roman! Thanks for the kind words.

    Indeed, the defensive stats make the team seem to appear better than they are. Some of the stats (corner 3s allowed, defensive rating) make the defense seem great. That's why during the Cavs game, Jalen Rose and the other commentators spoke about the Bulls as a defensive force the way they were during the Thibs era. As people who have watched closely know, this is not true.

    I wanted to tease apart what makes the defense worse than the numbers make it appear, and I hope I've done a good job of it!

  • In reply to Will Gottlieb:

    Another point in support of your thesis is that Bulls defense in Thibs' final year was weaker than in prior years, IIRC.

  • You have done your homework, we now need tallys on:
    Points lost when individual players don't block out, how many minutes individual players on the floor and are not in defensive position when the team is playing defensively vs..points scored by the opposing team, and the number of times a player failed to block shot or made a player change his shot while defending against the opposition.
    I aiming at tallys a player should recognize where his play should improve.

  • I've been shocked at the discrepancy between advanced defensive stats and what I'm seeing night in and night out.. good write up, thanks.

  • In reply to Chicagosportsguru:

    Opponents Field Goal Percentage is not an advanced stat in any way, shape or form, and the Bulls lead the league in that category.

    Defensive Efficiency is barely an advanced stat, anyone with any knowledge of the game now uses that instead of Points Per Game because it accounts for the fact that teams play at different paces.

    Take the Warriors, nobody would argue that they are anything other than an outstanding defensive team, right? They are 18th in the league in points allowed per game, because they play faster than most teams. But they are 3rd in the league in Defensive Efficiency, which is the only thing that matters.

    If someone wants to argue that the Bulls defense has been worse over the last month, they'd get no argument from me.

    Their Defensive Efficiency in January is 103.4 - which isn't surprising, since Noah only played 4 games in January.

    The good news is that their Offensive Efficiency went up in January by the exact same amount as their Defensive Efficiency went down, which also isn't surprising if anyone watched Noah trying to play offense this season.

  • Bulls blownout by Clippers! FO at sometime must concede end of season and let a proud Gasol go while the Bulls can get a quality player for him. Memphis for Green is one possibility.

  • In reply to penwit1:

    What if Gasol doesn't want to go because he still thinks this team is a contender? I agree 100% that if Gasol asks for a trade you do it, even if it's for nothing but expirings and a 2nd round pick.

  • In reply to Bullsville:

    Why would Gasol or anyone else still think this team is a contender? The fact that he's been busy hiring a new agent tells you what he thinks of this team.

  • The Bulls have no floor leadership directing play--Gasol helps but someone else should provide that skill when he is on or off the floor.
    I agree, it might be his call and Gasol should stay if he thinks this team has a championship in them next year and also be paid more-- but only if a healthy Noah returns--and if Noah is healthy and affordable. Gasol should not start only because of age and because we need him for the playoffs next year.
    The two centers together could be affordable. Noah won't be able to demand that high salary and because of prior injuries he has to prove his value--with a one year signing. When healthy, Noah is solid defensively and another offensive leader and presently the team on the floor misses his assists and play making-- getting teammates involved in a working offense while Rose was out. Before his first operation he was in the process of developing offensively. Some now say he had significant cartridge loss and bone was constantly rubbing against bone. Having two good centers is essential if Chicago has championship aspirations.
    The Bulls have no floor leadership directing play.

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