The humidor at Chase Field: 60 games in

Game 60 was last night’s 5-2 loss to the Phillies, so all stats below are to that point, and exclude this afternoon’s series finale against them, which is just getting under way as I type. After the last batch, which included games where 25 and 21 runs were scored, things have been rather more subdued over the last ten contests at Chase.

Runs scored and allowed

The high for this period was a mere 14 runs, during the 9-5 loss to the Rangers, and overall, 85 runs were scored. That’s fifteen fewer than over the same period last season, when exactly 100 men went into the scorebook. This is a return to what we’d have expected, after games 41-50 saw 33 more runs than in the pre-humidor era. But the effect is still considerably more muted than we saw at the beginning of the season. Dividing the schedule so far into these ten-game blocks, here is the year on year difference [negative = fewer runs in 2018]

• Games 1-10: -47 runs
• Games 11-20: -20 runs
• Games 21-30: -17 runs
• Games 31-40: -4 runs
• Games 41-50: +33 runs
• Games 51-60: -15 runs

Dividing the season thus far into two 30-game blocks, the first was at -84, and the second at +14. Quite a difference. Or if you prefer this in visual form, here’s the graph

All told, the average is now at -70, or 1.17 fewer runs per game than in 2018. The current pace is for 698 runs by the end of the year. This would be 105 down on last season, but perhaps surprisingly, would not be the lowest in franchise history. Over the 81 games at Chase in 2013, 681 runs were scored, so we are on track to pass that. However, the overall run environment is about two-thirds of a run per game higher this season than it was five years ago, so if we adjust the 2013 tally for that, we are still on track for a dampening effect.

Overall offense

Not much change in ERA at Chase, with the figure of 3.92 just four-hundredths down on what it was after game #50. If the aim was to turn Chase Field into a league-average park, I would say that’s mission accomplished, with the NL average ERA this season being 4.07. If this sustains, it would be the closest Chase ERA has been to league average since 2007 (4.42 vs. 4.44) and it the biggest shortfall since 1999 (4.37 vs. 4.57). Though here, the strength of Arizona pitching and defense plays a significant role, since they play more innings in Chase than anyone else, obviously. Below is a chart to show how this has ebbed and flowed over the years.

Home/road splits

A quick refresher. Over the first twenty years of the franchise, the team has always hit better at Chase Field than elsewhere. The amount has varied, from a mere three OPS points in 1999, to 136 points last year, but it has been a consistent feature for two decades. Of course, run environments have shifted dramatically in that time, as we went through the steroid era and came out the other side. But it’s the difference which we’re interested in, and from 1998 through 2017, here’s the sum total of the Diamondbacks home/road offense:

• Home: .269/.338/.442 = .781 OPS
• Away: .248/.315/.394 = .709 OPS

Now, let’s look at those same figures for the Diamondbacks’ performance at the plate in the 2018 season. We’ve played 60 games at home and 55 on the road:

• Home: .243/.324/.401 = .725 OPS
• Road: .231/.305/.401 = .707 OPS

This is interesting in a couple of ways. It shows the humidor impact, in that the road OPS is almost identical to the franchise pre-humidor average - only two points off. In contrast the home OPS is 56 points below the historical average in Phoenix. I also note the suppression seems not just to be of home-runs but also of batting average. Historically, the D-backs have batted 21 points better in their own park: this year, that difference is only 12 points. Fly balls that previously cleared (or banged off) the fence now dropping harmlessly into gloves? Could well be.

One more of these and then it’ll be an end of season wrap-up!