Entering the 2012 season, the Arizona Diamondbacks were the favorites to win the National League West. And why shouldn't they have been? This was, for the most part, the same team that won 94 games last year. With Justin Upton a year older, Paul Goldschmidt around for a full season, Stephen Drew making his return, and the rest of the gang contributing (Miguel Montero, Chris Young, Ryan Roberts, among others), there wasn't much reason to doubt that Arizona could repeat their success. Not to mention that the starting rotation would, at some point, get a boost from eventual call-ups Trevor Bauer and Tyler Skaggs.
The season hasn't gone as planned for the D'backs, though. Despite winning their past four games, Arizona sits at 48-48, six games out of first place in their division. A lot of that disappointment can be traced to Justin Upton, who has underperformed to this point. The young star has seen a sharp decline in his power numbers -- perhaps stemming from the thumb injury he incurred in April -- as his ISO has fallen all the way from .240 to .136; that said, Upton has quietly started to pick things up. Since June 13, he's hit .323/.392/.488 across 143 plate appearances (granted, that's come with a .376 BABIP).
As with Upton, the D'backs have seen underperformance from a couple other important position players, both of whom play on the left side of the infield... Ryan Roberts posted a 107 wRC+ last season while nearly reaching 20 homers and 20 steals, but has struggled thus far. Through 83 games, he boasts a .250/.306/.357 slash line (.290 wOBA). A slight uptick in his production is to be expected; ZiPS, for reference, projects a .314 wOBA out of Roberts over the rest of 2012. Additionally, as Stephen Drew continues to amass regular playing time, he'll probably start to return to form. Just a couple seasons ago, Drew was a 5-WAR player, and despite missing half of 2011, he still managed to post 1.9 fWAR.
On the pitching side of things, Arizona can bank on better results from Ian Kennedy, who just last year pitched to a 2.88 ERA. His peripherals haven't been much worse this season (his FIP has risen from 3.22 to 3.62), but the results have been -- as he currently owns a 4.20 ERA.
And as for Skaggs and Bauer, Arizona can still hope to get some kind of value out of them as they make their stretch run. Skaggs is currently four starts into Triple-A, and Bauer was sent back down after facing control problems, but both are close to ready to contribute at the major-league level.
Anyway, it's especially important to note that the D'backs haven't even been all that bad to this point. Consider that their Pythagorean record (50-46) is right in line with that of San Francisco (51-45) and Los Angeles (50-47). The Giants have a comfortable six-game lead in the NL West, but that's nothing that a late-season surge can't erase. And Arizona is even closer to seizing a wild-card spot, as they lie merely four and a half games out of the second wild card. Perhaps they haven't lived up to their expectations, but don't count the Diamondbacks out. They're still in the thick of the playoff hunt.