Some fun with run differentials:
Diamondbacks in August: 4-1, -2 run differential
Past 11 days: 8-2, -7
Since July 19: 13-4, -2
Post-ASB: 16-7, +1
Season total: 63-50, -29
Whenever something unexpected happens, it's a basic human impulse to find the cause. Sure enough, whenever a team outperforms its run differential like this (the Mariners have been a chief offender all season long), you see explanations pop up everywhere: they play good "small ball", the bullpen is winning the close games, etc. These things do have a small effect on a team's winning percentage in close games, so why do these overachieving teams tend to regress to the mean?
The problem is that these factors explain maybe 10% of the variance in W-L records, much like the reasoning behind David Ortiz's "ability" to hit in the clutch. Players cannot suddenly become .700 hitters in the ninth inning--if so, why are they being so lazy for the rest of the game?--and teams cannot employ strategies that allow them to win two-thirds of their close games despite a negative run differential. A team can be built to win maybe 55% of its close games, but the rest must be attributed to variance.
Check out BP's adjusted standings. The Diamondbacks are in last place in the NL West (yes, behind the Giants) and languishing with the league's bottom-feeders. What happened to the team I picked to win the NL West?
Well, they're winning, but not the way they were supposed to. Randy Johnson, who may have been the best pitcher in the NL this year when healthy, gave Arizona 100 less innings than expected. Chris Young and Stephen Drew can't get on base, Carlos Quentin has been worthless, and the bench that looked excellent at the start of the year has churned out a .511 OPS from Alberto Callaspo to go with Scott Hairston's .659. The Diamondbacks rank 29th in team OBP in a hitter's park, ahead of only the PETCO-hamstrung Padres.
Eric Byrnes is the only hitter who has delivered more than expected, but the pitching staff has plenty of success stories. Brandon Webb's ERA sits at 2.92, Doug Davis' at 3.88, and the bullpen features four regulars at 2.80 or below, plus Juan Cruz at 3.38. They've pitched especially well in close games, and the hitters have performed in the clutch. I'm not positive that the D-Backs lead the league in walkoff wins, but I would be suprised if they didn't.
So, will Arizona continue this ridiculous run? Probably not. On the plus side, they've now built a decent-sized lead and could limp their way to 88 wins and a playoff berth by playing .500 ball from here on out. Plus, the roster is loaded with young players who are likely to show some growth in the second half.
We're at a point in the season where a head start is usually more important than having the better team, Yankees be damned. The Padres are probably still a slight favorite (plurality) to take down the West, but it's a fun time to be an Diamondbacks fan, even if this squad turns out to be far inferior to the 2008 version.