Sunday’s loss to the Portland Trail Blazers dropped the Bulls to a  mediocre 5-5.

That’s not what these Bulls — who have owned the league’s best record the past two seasons — are accustomed to.

There are three main reasons the Bulls are struggling:

1. No Derrick Rose
2. Decline in Defense
3. Reduced Bench Performance

The Derrick Rose situation is an obvious one.

As I mentioned yesterday, the defense has been a major disappointment. According to Basketball-Reference, the Bulls currently rank 10th in Defensive Efficiency at 102.0 points surrendered per 100 possessions. You might be thinking: “Top 10 isn’t that bad.”

It is for Tom Thibodeau’s Bulls.

In 2010-11, the Bulls ranked second in Defensive Efficiency at 100.3. In 2011-12, they were again second at an even better 98.3.

This season, they’re giving up almost four more points per 100 possessions than they did last year. And it has been far worse than that over the past four games during which they’ve had a horrific defensive rating of nearly 112 points surrendered per 100 possessions.

For perspective, the Phoenix Suns are currently dead last in Defensive Rating at 109.7. In other words, over the past four games, the Bulls have been a few points per 100 possessions worse than the league’s worst defensive team.

The third factor in Chicago’s ho-hum start has been the bench production compared to the past two seasons. I have provided bench statistics from the past three seasons below. These numbers were obtained from Hoopstats. League ranks are in parentheses. Pay particular attention to the following stats:

Eff = NBA Efficiency recap = ((Points + Rebounds + Assists + Steals + Blocks) – ((Field goals attempts – Field goals made) + (Free throws attempts – Free throws made) + Turnovers))

Deff = Efficiency Recap Difference = Efficiency Recap – Opponent’s Efficiency Recap

2010-11
Pts: 26.6 (25)
DReb: 10.0 (15)
OReb: 3.8 (14)
TReb: 14.0 (13)
Ast: 6.3 (15)
Stl: 2.9 (7)
Blk: 2.5 (2)
FGP: 44.6 (13)
3P%: 38.4 (5)
Eff: 33.7 (15)
Deff: 8.0 (2)

2011-12
Pts: 29.2 (23)
DReb: 10.4 (17)
OReb: 5.3 (2)
TReb: 15.7 (10)
Ast: 6.6 (13)
Stl: 2.4 (25)
Blk: 2.7 (2)
FGP: 44.2 (7)
3P%: 40.5 (2)
Eff: 36.0 (11)
Deff: 8.7 (6)

2012-13
Pts: 29.8 (24)
DReb: 8.5 (24)
OReb: 3.4 (21)
TReb: 11.9 (26)
Ast: 6.4 (17)
Stl: 2.3 (24)
Blk: 2.3 (8)
FGP: 42.2 (19)
3P%: 34.4 (13)
Eff: 32.3 (24)
Deff: -1.2 (21)

As you can see, there have been notable (and significant) drop offs in rebounding (especially offensive rebounding), blocked shots and three-point shooting.

However, the most glaring change is the efficiency differential, which has fallen from from Top 10 to Bottom 10. Whereas the Bench Mob regularly outperformed their counterparts, the current bench is usually in the red.

It’s not hard to see what has happened. Omer Asik is killing it for the Rockets. Ronnie Brewer is playing extremely well for the Knicks and rocking a Player Efficiency Rating of 17.1. C.J. Watson is playing about as well as he ever has (and is even rocking a career-high in Effective Field Goal Percentage).

The current unit is no Bench Mob.

It’s worth noting that Jimmy Butler has been playing extremely well. He’s shooting a blistering 60.7 percent from the field and 92.9 from the free throw line. Those are the best marks on the team. He’s also playing solid D and sporting the team’s second best PER of 18.2.

Nate Robinson has been pretty good too. Nate is scoring 12 points per game, he’s shooting 40 percent on threes, and his PER is third on the team at 17.6. That said…he’s undersized and gets taken advantage of on defense.

As for the rest…

I noted this yesterday: The real Taj Gibson hasn’t shown up yet. His numbers have taken a nasty downturn since last season. He’s shooting a career-low 41 percent. He’s averaging only 4.3 rebounds. His Player Efficiency Rating (13.6) hasn’t just dropped since last year (16.9), it’s currently a career-worst.

Similarly, his Offensive and Defensive Rebounding Percentages (8.7 and 12.3) are career-lows and well beneath his career marks (11.4 and 18.5). Taj is blocking more shots — from 1.3 in each of the last three seasons to 1.9 this year — but he’s regressed significantly in virtually every other area.

Don’t get me wrong. Gibson is still hustling and playing defense that ranges anywhere from good to great. But on the whole, he isn’t playing nearly as well as the Bulls are accustomed to.

Past that, “designated shooter” Marco Belinelli is converting a career-low 37.8 percent of his field goals and looks perpetually lost on both ends of the court; Nazr Mohammed is shooting 7.1 percent from the field and looks ready for the glue factory; rookie Marquis Teague has played an average of six minutes in only five of the Bulls’ 10 games; and Vladimir Radmanovic has a PER of -0.4.

So let me sum this up: No superstar, worse defense, drastically reduced bench. From that perspective, maybe we should be grateful the Bulls are .500.

There were a lot of positives in the Bulls’ home win over the Charlotte Bobcats. Joakim Noah scored a career-high 21 points (on 10-for-12 shooting) while grabbing a game-high 16 rebounds (including 6 on the offensive end) and blocking 4 shots. John Salmons finally broke out of his slump with a big-time performance (game-high 27 points on 9-for-16 shooting to go along with 7 rebounds, 6 assists, 3 steals and a block). As a team, Chicago had their best shooting night of the season (50 percent), played solid team defense (the ‘Cats shot 39 percent), won the rebounding battle 44-38 (while grabbing 15 offensive boards), outscored Charlotte 19-5 in fast break points, and won the Battle of the Paint (36-26).

So…why didn’t the Bulls win this one by a lot more than just three points?

Well, there were some negatives, too. Such as letting the Bobcats snare 16 offensive rebounds of their own. The Bulls were also careless with the ball, giving up 28 points off 21 turnovers (led by Derrick Rose’s game-high 7 TOs). They also bricked nine of their 22 free throw attempts, including five straight in the final 1:20 when they were trying to clinch the game (two by Joakim, two by Luol Deng and one by Salmons). Chicago also had trouble getting a hand in the face of Charlotte’s three-point shooters. The ‘Cats came into the game shooting 28 percent as a team, but they went 12-for-29 last night (41 percent). And that number was much better before the Bobcats were forced to start gunning for a comeback in the final minutes.

The point is: I was both encouraged and worried by the win. To win in the NBA, you absolutely must protect your defensive backboards, take care of the ball and hit your free throws. The Bulls didn’t do any of those things. But they won anyway. Which is nice, but I sure hope Vinny Del Negro wrote a few of these things down in his notebook so the team can work on them during their next practice.

Slump Buster:
Salmons didn’t break out of his slump by hanging out on the perimeter and jacking up threes until he got hot. He was aggressive, driving hard to the hoop and canning four layups and earning a game-high nine free throw attempts (including a couple And-1s). The Fish Man really is at his best when he forces the action on drives. When he does that, he gets his defenders on their heels, which opens up the space he needs for his jumper. Hopefully, this is a trend that will continue.

Oh Jo!
Noah joined a semi-exclusive group last night, becoming the the third player in the last six seasons to have at least 20 points, 15 rebounds, four blocks and shoot 80 percent from the field in a win. The other two? Kevin Garnett (versus the Dallas Mavericks on March 21, 2001) and Shaq (against the Milwaukee Bucks on March 21, 2004).

On offense, Jo did most of his damage via offensive rebounds (8 points on four tipshots) and dunks/layups. But he also hit a couple jumpers (from 14 and seven feet out) and knocked in a nifty left-handed hook shot from the baseline. I wouldn’t go so far as to say Noah has become scoring force, but he has added a few aspects to offensive game. And that’s a good thing. The only blight on Joakim’s evening was the two missed free throws at the 1:20 mark.

Dang, Deng:
Luol may not have shot very well (6-for-17), but he he went 4-for-8 in the fourth quarter, hitting from 19, 21, 21 and 23 feet out. Deng also grabbed two offensive rebounds in the fourth, one of which led to a big three-pointer by John Salmons. For the game, Luol grabbed 11 rebounds (to go with his 14 points), six of which were offensive. I bring this up because Deng has been crashing the boards with a vengeance so far this season…and he’s averaging 9.8 per game. He may not be shooting all that well (44 percent), but he’s working really hard.

Wipe that butter off your fingers, Derrick:
It’s not a good thing when your All-Star-in-the-making point guard dishes only 4 assists while committing 7 turnovers and finishes with the worst plus-minus score (tied with James Johnson) on the team (-7). Derrick was careless with the ball last night, and it hurt the team. That’s a big reason why he played fewer minutes (30) than Kirk  Hinrich (33), who dished 7 assists versus 4 turnovers. It’s all about playmaking, and that’s the area in which Rose needs to improve the most.

On the bright side, Rose has clearly added a nice little pull-up jumper to his offensive skill set. Last night, he went 5-for-9 on his outside shots. He seems to like that area near the free throw circle on the left-hand side of the floor.

Not much in the reserve tank:
With Tyrus Thomas out for a month or more, the Bulls are suddenly a little weak off the bench. Deng, Noah and Salmons all played 40-plus minutes (47, 41 and 43, respectively). And Chicago got only 12 points out of their reserves (Hinrich scored 9 on 3-for-10 shooting and Brad Miller added 3 while Jannero Pargo and James Johnson went scoreless). This worries me a lot, especially since the Bulls will round out the month on a six-game road trip versus the Kings, Lakers, Nuggets, Blazers, Jazz and Bucks.

TrueHoop Network:
Brett from Queen City Hoops: “Meritorious Player: Tough call – Boris Diaw had a decent night with 20 points, 7 rebounds, and 5 assists…but 6 turnovers. Raymond Felton led the Bobcats with a +/- of +11 and had 10 assists…but he shot just 5 of 17 from the floor. Tyson Chandler had 13 points on 5 of 8 shooting and 7 rebounds in 28 minutes…and a brutal -13 for the night as Joakim Noah posted a career high 21 points (and 16 rebounds was a good night’s work). Pick one – they all had their faults tonight.”

Extras:
Recap, Box Score, Play-By-Play, Shot Chart, Photos.

Turns out the bench was pretty darn important last season.

While sifting through the incredible amount of data over at 82games.com, I came across the NBA Team Starter/Reserve stats page for the 2008-09 season. Check this out:

Last season, the Bulls bench ranked 13th in points per 100 possessions (106.3), 10th in rebounds per game (14.3), ninth in points per game (31.0), tied for 7th in assists per game (6.9), tied for fourth in steals per game (2.7), and an amazing third in the league (behind Boston and Utah and ahead of the Lakers and Cleveland) in net points (+462). That’s some pretty impressive bench production! And note that the four teams around them in net points were a combined 241-87…that’s a winning percentage of 73 percent. So bench-wise, the Bulls were in elite company in 2008-09.

Now check out how the starters ranked in comparison: 19th in points per 100 possessions (105.7), 17th in rebounds per game (27.8), 13th in points per game (71.2), 24th in assists per game (14,2), 19th in steals per game (4.7), and a dreadful 21st in net points (-577). The only teams that ranked below them in net points were New Jersey, New York, Golden State, Minnesota, Memphis, Oklahoma City, Washington, Sacramento and the L.A. Clippers. Note those were all bottom-feeding lottery teams. Further consider the fact that those squads had a combined record of 221-517 (a winning percentage of 36 percent).

So it seems that the Bulls’ bench production more important than we might have guessed…and that the relative productivity of the starters was actually much worse. If the Bulls are going to be more than a seventh or eighth seed this season, they have to continue to get strong performances from their reserves while getting much better total production from the starting unit. If I had to guess, I’d bet that will start (if it happens) with defense.