So, what's this whole humidor thing about, anyway? What are the effects of storing baseballs in a 40% humidity environment?
The biggest effect you would expect is that heavier balls hit in the air wouldn't carry as far, and that appears to be the case. The most obvious impact is in the home-run rate at the park:
(Note that the numbers for the last five seasons do not include interleague games. I was working with the STATS Major League Handbook's park data, which sensibly excludes those games.)
AB/HR 2002: 32.4 2001: 22.0 2000: 24.0 1999: 19.7 1998: 27.4 1997: 23.5
Home runs are almost 50% harder to hit at Coors Field this year than they were last year, and about 40% harder to hit than they've been over the past five seasons. That's a remarkable dropoff, almost like moving into a completely new park.
Where are all of these home runs going? Into gloves, mostly. I pointed out in Baseball Prospectus 2002 that simply not striking out at Coors Field made you a .378 hitter with a .649 slugging average. This year, players who put the bat on the ball are down to a .342 batting average and a .544 slugging average. That dropoff, particularly in slugging, is huge.
It's not just the home runs. Last year, a ball in play at Coors turned into a double or a triple once every 10.1 times. This year, that figure is once every 12.4 times. On the other hand, the rate of singles per BIP is up slightly, from 4.11 to 4.25. Essentially, extra-base hits are being traded for a lot of outs and a few extra singles (perhaps the result of outfielders playing deep in what is a large Coors Field pasture).
Just how many more outs? According to the Defensive Efficiency statistic, balls put in play at Coors are being turned into outs 68.4% of the time. This isn't a high figure—it's well below the league average of 70.4%—but it is miles beyond what we'd seen at Coors previously:
DE 2002: .684 2001: .658 2000: .656 1999: .651 1998: .659 1997: .658
For years, balls traveled farther, faster, and landed more quickly in Denver than they did everywhere else. Now, they're behaving more the same way as they do at ballparks around the country. After nine seasons of high offense at high altitude, it appears that the simple act of storing baseballs in a moist environment has essentially turned Coors Field into a slightly-above-average park for run scoring, shaving five runs a game off of the average match.
Isn't that an indication that the idea has overshot its mark?
I've said all along that the people who wanted to correct for Coors Field—pressurized domes and special baseballs and the like—were doing so for aesthetic reasons. There's a segment of fans and writers who were weaned on a low-offense style of baseball and who become offended at the idea of a place where the average game has 15 runs scored.
Personally, I loved the "old" Coors Field. Not because I'm some simpleton who needs to be entertained by home runs, but because it was different. Baseball is baseball no matter where it's played, but baseball at altitude was a game unlike that I'd ever seen—yes, I'm too young to remember 1930, or the Baker Bowl—and that made it fun. Variety is great for the game; having a Coors Field is just as good for it as having a Dodger Stadium or a Comerica Park is. The different ways in which teams have to try and win in these places one of the things that makes the game so enjoyable.
Yes, I know that the conditions presented some challenges for the Rockies as far as keeping pitchers healthy and assembling a roster, but many of those problems still exist. The strikeout and walk numbers of Rockies pitchers are still unimpressive (13th in the NL in Ks, ninth in walks allowed), because the thin air still makes it difficult to throw breaking stuff. The lack of oxygen in the air is still going to create problems with stamina and make it harder to recover from injuries.
All the humidor has done is made the game more homogenous. It has turned one of the game's most unique environments into just another place where baseball is played. Maybe that's a good thing to some people, but to me, it's sad, and something I hope the powers that be will change.