As basketball fans, we tend to over-analyze our team's performance from game to game, particularly on the defensive end of the court. But much of the variation we see in the outcome of games can be attributed to simple luck. Over the course of the season, luck evens out and the teams with the best offenses and defenses establish themselves by their record of performance. But in any given 3 or 4 game sample, luck can easily be a big enough factor to obscure much of what we think we're seeing.

Take for example the last two Blazer games. In Houston, the team gave up 111 points to the Yao-lessRocketsand were lambasted for their defensive performance. In Oklahoma City last night, the Blazers held theThunderto just 74 points and received praise for their defensive effort. While I think it's probably true that the Blazers played marginally better defense last night, luck certainly amplified the difference.

The primary (but not exclusive) way that luck manifests itself in basketball is in an opponent's outside shooting percentage, which is best represented in the traditional box score by the 3 point percentage. While it's certainly true that good defensive play (such as getting hands in shooter's faces, not leaving good shooters open, etc.) can reduce an opponent's outside shooting percentage on average over the course of a season, for individual games, much of the variation in shooting percentage is due to luck. Sometimes shooters are hot and other times they aren't. Over the course of a season, 3-point shooting percentages across the league fall within a relatively narrow band. Last year, the team with the best percentage (Boston) made 39.7% of its threes. The worst team (PHI) made 31.8%. (Portland was 4th at 39.3%). Defensively, the range is similar. The best team (Cleveland) allowed opponents to shoot 33.3%, while the worst team (SAC) allowed opponents to shoot 40.6%. (Portland was 19th at 37.4%).

So even the best defensive team allowed opponents to make a third of their threes, and the best offensive team made only 40% (just 7 percentage points higher) . What that means is that, in an individual game, when a team makes 50% of its threes (as Houston did the other night) or 20% of its threes (as OKC did last night), much of that variation is attributable to luck, not the defense. Had either Houston or OKC had an average night shooting from downtown, the outcomes of both of those games might well have been different.

When a team is hot from outside, it has a huge effect within the game. Defenders are forced to play farther out which opens up space and allows for easier dribble penetration and interior scoring. When a team is cold from outside, the opposite happens. Defenders cheat back and clog up the middle. They intercept more passes and are better able disrupt penetration and post scoring. Good defenses can suddenly look terrible when the other team is hitting threes and mediocre defenses can suddenly look brilliant when the other team's shooters go cold.

That's why you want to be really careful when assessing a team's performance on a game-by-game basis. Your judgment, given the small sample size, can easily be skewed by the role of luck. The reality is that Portland wasn't as bad on defense against Houston as the score and stats suggest and Portland wasn't as good defensively against the Thunder as the score and stats suggest. This is why you play a whole season.

The season is still very young and we don't have a whole lot of data to work with yet. We should get a better sense of where the Blazers are both offensively and defensively after another week or so.