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December 2, 2009

The Disappearing Portland Defense

Filed under: Uncategorized — Kevin Pelton @ 6:00 pm

Tensions are running high in the Rose City in the wake of a three-game Portland Trail Blazers losing streak, with two of the three games played at the Rose Garden, where the Blazers are usually tough to beat. While Portland is working through a variety of issues on the offensive end, including the emergence of Greg Oden and the addition of Andre Miller, the difference lately has been on defense. As recently as last Friday, Portland was second in the league in Defensive Rating. The three poor games have seen the Blazers slip all the way to seventh.

Benjamin Golliver of Blazersedge (with whom I discussed some of the team’s issues on the most recent Dontonio Wingcast podcast, along with our contest to win a free copy of Pro Basketball Prospectus 2009-10) questioned the legitimacy of the lofty early ranking based on the weak slate of offenses faced by the Blazers. Let’s take a look.

What this chart shows is two Defensive Ratings for the Blazers for each game–one the standard points allowed per 100 possessions (in black), the other adjusted for the quality of the opponent offense (in red). I set the latter to league average (107.9 points per 100 possessions) to compare it on the same scale. As you can see, more often than not the red is higher because Portland has in fact gotten a break in terms of strength of schedule in the early going (the average Offensive Rating of opponents has been just 105.9). Nonetheless, the team’s defense was strong through a win on Nov. 21 against Minnesota.

Using the adjustments shows it has really been a five-game trend of poor defense for the Blazers, one masked slightly by the fact that Chicago and especially New Jersey are below-average offenses (as well as by dominant offense in an easy win over the Bulls). Before the last five games, Portland’s adjusted Defensive Rating had been above 110 just twice all season. It has been worse than that mark each of the last five games.

Why the change? The difference is almost all in terms of shooting. Check out the Four Factors plus shooting percentages as broken down by the first 15 games and the last five.

Split       2P%    3P%   eFG%  DReb%  FTA/FGA    TO%

First 15   .436   .315   .443   .752   .308     .101
Last 5     .526   .446   .547   .746   .282     .129

The Blazers have been forcing fewer turnovers, but they’ve offset that to some extent by sending opponents to the line less frequently. For the most part, teams are just shooting lights-out against Portland, both inside and outside the arc. What I don’t have is a good explanation for why this is happening.The team’s rotations have clearly not been nearly as crisp lately, but that to me is more of a symptom than an underlying cause.

The only dramatic change to personnel in the span, save LaMarcus Aldridge missing last night’s game, was the shift back to a traditional starting lineup with Martell Webster at small forward instead of the smaller unit with Andre Miller alongside Steve Blake in the backcourt. For whatever reason, the Blazers have defended better with the undersized group despite the fact that it seemingly makes the team worse defensively against both wing positions.

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