We wouldn’t expect the Arizona Diamondbacks to be good anywhere; even so, their futility at home is something of anomaly. Through 40 home games, the Dbacks are 13-27, whereas on the road they are a .500 ballclub at 18-18. What gives?
Below I’ve provided some basic hitting and pitching splits for the Dbacks. At the team level, the differences between home stats and road stats are not so great.
Arizona hits better at home by all the typical measures–batting average, on-base percentage, slugging. Even so, they score more runs per game when they are on the road. The only way I can sensibly reconcile those two facts is to guess that the Dbacks have a poor record of hitting with runners on base when they are at home. They get more hits at home than they do on the road, but they don’t string them together well. Lately people have taken to calling this “cluster luck.” Since we are less than halfway through the season and it doesn’t make much sense for a team to hit relatively better but score relatively less, I’d say luck is probably a primary factor.
Even so, Arizona’s home offense is disappointing in their own right. Chase Field in Phoenix is consistently one of the best hitter’s parks in the majors. You see how Diamondback pitchers fare worse at home, but their hitters this year have not taken advantage. Gerardo Parra at home has a .292 OBP and a slugging of .327. Aaron Hill is another sub-.300 OBP fellow. Martin Prado and Miguel Montero can’t crack .400 slugging at home, and they occupy the heart of the lineup. Of Dbacks with more than 50 home plate appearances, only Paul Goldschmidt, the injured A.J. Pollock and Chris Owings are hitting the ball with any authority. And no one but the behemoth Goldschmidt has hit the ball well both at home and on the road. This is a team that relies pretty heavily on veteran production. Cody Ross, Prado, Hill and Montero are all 30 or older and constitute half of the everyday lineup. There are no obvious replacements in the farm system, so the hope is this is a bump in the road and not the start of inevitable decline.
On the pitching side, the most prominent disparity between home and road is found in slugging percentage. Both figures are high for any pitching staff, but .447 is just absurd, about equal to one Adam Dunn or Jay Bruce. It is likely Dbacks pitchers have suffered from some bad cluster luck in their own right, seeing how runners reach base less (.318 vs .335 OBP), but score more.
Let’s look at some individual pitchers. Bronson Arroyo has 37 innings pitched at home with a 4.86 ERA, compared to 49 and 3.49 on the road. One quick look at BABIP tells you that disparity probably isn’t his fault–.331 at home, .266 on the road. Another player similarly beaten down by batted-ball luck is Wade Miley: 56.2 IP, 5.40 ERA, .304 BABIP at home; 44.2 IP, 3.63 ERA, .267 BABIP on the road. These two starting pitchers are among the most durable in baseball, and they will probably pitch through the end of the season just fine, though their poor starts will keep their numbers inflated.
We can use the figures for runs scored and runs allowed to determine Arizona’s Pythagorean records both at home and away. At home, Arizona’s runs scored and runs allowed fit the profile of a 15-25 ballclub, only two wins better than they are presently. On the road, they ought to be 16-20, two wins worse. Not all stats carry hope.