There's a page on Wikipedia titled "Regression toward the mean." On that page, they use this to explain what it is:
μ ≤ E[X2 | X1 = c] < c,
So you can be damned sure that I tuned out whatever I was reading and started thinking about Kazuo Ishiguro novels or something. But the page came up in a Google search because I was looking for the Plexiglas Principle, and the Bill James creation is cited in the page about regression. Jonah Keri expands on it for a recent Grantland column:
The crux of Plexiglas is this: A team that improves in one season tends to decline the next, and vice versa. It was an easy idea to understand, but a tough one to believe. We human beings are hard-wired to hate randomness. So we look for patterns in everything. Thus a team that wins 75 games one year and 81 the next is perceived to be on the rise, destined for greater things. A team that slips from one season to the next is on its way down, headed for a stretch of lean years. Fans make this mistake, writers and prognosticators make this mistake … even MLB general managers make this mistake.
The 2010 Diamondbacks lost 97 games. Their bullpen gave up a run as I was typing this. I don't know how. I told you, I'm not a math or science guy. Go ask Alfred Einstein. But they just gave up another run, and they're threatening to lose their 98th game of the 2010 season well over a year after it ended.
The 2011 Diamondbacks won 94 games and were an extra-inning win away from advancing to the NLCS.
When a team improves that much in one season, it's safe to assume, knowing nothing else, that they'll give back some of the gains the next season. And there are some troublesome things about the Diamondbacks' roster: There was nothing in Josh Collmenter's professional career that suggested he would have that kind of command or success; Willie Bloomquist is their leadoff hitter until Stephen Drew returns from a serious injury; when the team spent money in the offseason, it was in an inexplicable move to make the lineup and defense worse; when pitchers like Daniel Hudson and Ian Kennedy take a leap forward like they did, remember the Plexiglas Principle applies to players too.
So if you squint, the Diamondbacks look like a team that could bump into some Plexiglas. Here's why they might not, though:
1. The rest of the NL West spent the offseason sitting in the corner, eating paste
Oh, that's not entirely fair. The Giants procured Melky Cabrera, who could, I guess, repeat his fine year. The Padres traded for Carlos Quentin. The Rockies traded for Jeremy Guthrie and signed Michael Cuddyer. The Dodgers acquired Mark Ellis, Jerry Hairston Jr., and Adam Kennedy. Yeah, that's right. All three. For some reason.
But stop me when you get to the name that knocks you over, that makes you think, "Man, now that player will make his team oodles better." Maybe one of the teams will get better because they're healthier, or maybe there will be strong, unexpected performances from unexpected players. The Diamondbacks don't have a lock on anything, mind you. But it's hard to see where their competition got substantially better.
2. Justin Upton is a man-beast who will destroy us all
So good. He is going to be so good. He cut his strikeout rate at the same time he reached career high in home runs, which just swell. The most impressive part, though, is that he was 23. I'm not sure if it's entirely smart to just assume that he keeps getting better and better, but it's possible. He's the same age as Domonic Brown, Brandon Belt, and Dustin Ackley -- all players who haven't done all that much yet, but who are still thought highly of. Upton is close to 100 home runs for his career. He's already made adjustments and readjustments. And he still has the box of tools that made him the #1-overall pick.
3. Daniel Hudson and Ian Kennedy are that good. Or, close to it
Kennedy cut down on his walks substantially, and he was pretty good in the season before. Hudson has been stellar at every level he's pitched at in his pro career. Maybe you can assume that young hitters will get better as they approach their age-27 peak, but you can't assume that pitchers will just keep getting better and better and better. Tim Lincecum didn't. Cole Hamels didn't. They didn't just keep improving and morph into '68 Bob Gibson.
But they didn't get worse, either. I'm not seeing the flaws in Hudson's or Kennedy's game that make them automatic candidates for serious regression. They pitched a lot more innings than they ever have before, but the Verducci Effect has been mostly debunked. I can see the argument that suggests that Collmenter might get worse, but even if that's the case …
4. There are pitching prospects who are ready to step in if the rotation falters
Trevor Bauer is probably the most well-known of the bunch, but Tyler Skaggs is an excellent prospect as well. If Collmenter or Joe Saunders struggle, it's not like the Diamondbacks have to go with Miguel Batista, or something.
5. Jason Kubel is … well, I'm not sure about that, actually
The Diamondbacks had a one-time prospect hit .292/.357/.427 in his age-24 season, winning a Gold Glove and stealing 15 bases in the process. They chose to replace him with a guy who hit .273/.332/.434 and plays questionable defense. Like, they're paying $16 million for the swap. Feels like their hubris should be punished by whatever Greek god pays attention to this stuff.
So it isn't all roses for the Diamondbacks. But there isn't a spot on the roster that you can point to and say "There! That's where they got worse! That's where the house of cards will come down!"
No, no, Willie. Even you don't make that much of a difference. Plus, Stephen Drew should be back at some point. The Diamondbacks were a complete team in 2011. They should be a complete team in 2012. If anything, the fluke season was probably 2010.
Coulda Shoulda Woulda (Hole they didn't fill)
They probably could have picked up another left fielder or utility infielder. You never know when you'll run low ...
This is probably an N/A. They probably over-committed to Aaron Hill based on his hot finish, and Ryan Roberts might be a better utility player than a starting third baseman, but the Diamondbacks didn't have a lot of needs.
Two of them: Paul Goldschmidt has monstrous, prodigious power, and he dramatically improved his strikeout rate while advancing to double-A last year. But he still popped up straight from double-A and did a once-around the league. There's a chance that the rest of the league will figure something out the second time around.
Trevor Cahill had a 2.31 ERA through May of last year; he had a 5.28 ERA after that, though he did rebound to have a scoreless seven-inning stint for his last start of the season. Though it was against the Mariners. Forget I mentioned it. He's probably not as good as he was in 2010, and he's probably not as bad as he was in the second half of last season. Also worth noting: He just turned 24. He can get a lot better, too.
Parra retakes his job at some point. Trevor Bauer wins the Rookie of the Year while screwing Giants, Dodgers, and Padres hitters into the ground. Lyle Overbay starts more than he should.
Kansas City Royals
Los Angeles Dodgers
Los Angeles Angels
New York Mets
New York Yankees
San Diego Padres
Tampa Bay Rays
San Francisco Giants
St. Louis Cardinals
Toronto Blue Jays