We've been hearing it the past month from Bulls coach Scott Skiles: The Bulls' defense is slipping. They once had a 26 game streak of holding opponents under 100 points, and since then have allowed that benchmark 11 out of their last 15 games.
But while that was it concerned I wondered how much of this was due to the better competition in that more recent stretch than they had in January. How much of this perceived lapse in defense was real or was it merely playing against a better offensive team that caused the final point total to look worse than it truly was?
So what I tried to do was look at a by-game analysis of how Bulls' opponents fared relative to their season norms. The stat used for comparison is offensive efficiency (OE), which is a fancy way of saying points-per-100-possesions.
(By-game calculations were done with reference to Kevin Pelton's stat page, and season stats are always ready for you at Knickerblogger.net.)
| Date | Opponent | Pts | Poss | OE-gm | OE-season | Diff |
| 1/5 | @NO | 89 | 99.2 | 89.7 | 96.0 | -6.3 |
| 1/7 | UTA | 78 | 95.5 | 81.7 | 93.0 | -11.3 |
| 1/8 | BOS | 91 | 95.8 | 95.0 | 104.0 | -9.0 |
| 1/10 | GS | 85 | 100.7 | 84.4 | 98.5 | -14.1 |
| 1/12 | PHI | 78 | 98.0 | 79.6 | 100.5 | -20.9 |
| 1/15 | NY | 84 | 93.9 | 89.5 | 102.2 | -12.7 |
| 1/17 | @NYY | 86 | 89.9 | 95.7 | 102.2 | -6.5 |
| 1/19 | @BOS | 92 | 95.2 | 96.6 | 104.0 | -7.4 |
| 1/21 | ATL | 85 | 93.2 | 91.2 | 96.2 | -5.0 |
| 1/22 | @DET | 89 | 85.5 | 104.1 | 102.2 | 1.9 |
| 1/24 | @ATL | 82 | 95.0 | 86.4 | 96.2 | -9.8 |
| 1/25 | DEN | 107 | 101.3 | 105.6 | 100.2 | 5.4 |
| 1/27 | CHA | 93 | 91.9 | 101.2 | 97.0 | 4.2 |
| 1/29 | BOS | 101 | 97.0 | 104.1 | 104.0 | 0.1 |
| 2/1 | @NJ | 107 | 94.9 | 112.8 | 96.7 | 16.1 |
| 2/5 | @MIA | 108 | 105.6 | 102.3 | 108.3 | -6.0 |
| 2/8 | DAL | 100 | 100.2 | 99.8 | 106.8 | -7.0 |
| 2/9 | @HOU | 105 | 91.0 | 115.4 | 101.4 | 14.0 |
| 2/13 | @MIN | 83 | 85.0 | 97.7 | 104.4 | -6.7 |
| 2/15 | SAC | 102 | 103.2 | 98.8 | 106.5 | -7.7 |
| 2/16 | @TOR | 115 | 97.1 | 118.5 | 103.8 | 14.7 |
| 2/22 | MIA | 101 | 105.0 | 96.2 | 108.3 | -12.1 |
| 2/23 | @CLE | 100 | 96.0 | 104.1 | 103.8 | 0.3 |
| 2/25 | WAS | 90 | 98.7 | 91.2 | 103.9 | -12.7 |
| 2/26 | @CHA | 90 | 93.1 | 96.7 | 97.0 | -0.3 |
| 3/1 | HOU | 119 | 93.2 | 127.6 | 101.4 | 26.2 |
The games in red are ones in which the Bulls opponent outperformed their normal offensive efficiency. As you can see there has been a lot more red recently, so in essence Skiles was right. From the first game I looked at on 1/5 (at New Orleans, picked because it was the first in the stretch where they faced the poorer teams) until the 1/24 rout of Atlanta, on average the Bulls forced their opponents' OE to be -9.2 points lower than their season average. Behind that defense they went 10-1. In games following until the game which shall not be mentioned, that number fell to actually have teams have a 1.8 point increase, and the record a less impressive 9-6.
But this mini-study still illustrates the point I was trying to make, that being not looking at giving up 100+ points as the sure indicator of bad defense. For example, in both games against Miami the Heat scored 100, but each time the Bulls defense actually held them to a lower offensive efficiency than their season average.
That said, there is no doubt that the Bulls defense isn't what it was when they went on their winning streak(s), no matter who was on the schedule.
[I'll be at THE Ohio St. University on Sunday to watch the Illini try and finish the regular season undefeated. So there may or may not be a Carnival of the NBA post ready by Monday morning, we'll see. Either way, send me your submissions by Sunday night]