NOTE: All numbers as of the All-Star Break. I did most of the work prior to Friday's games. But all numbers as of the All-Star Break.
Something I enjoy looking at is the spread between a team's ERA, FIP and xFIP as it gives and idea of what teams are getting lucky and gives of an idea of who may come back down to Earth (or make a charge in the win column). Seeing that we’re over halfway through the season, now is a good time to dive into this.
Let’s get this out of the way right away. When looking at team pitching staffs, ERA matters a lot. Last year, wins were most highly correlated to ERA—not FIP, not xFIP, not K/9, not WAR—it’s ERA. A good ERA = wins. This seems intuitive, but it’s important in this day in age, and there is a lot of good info in FIP, xFIP, K/9, and they are pretty highly correlated, but it’s ERA is more highly correlated*. Anyway, here are the correlations for 2012 team pitching (source for all this is fangraphs).
*As always, correlation does not imply causation.
Okay, with that out of the way... let’s go to the spreads!
xFIP and ERA: The best differentials
xFIP and ERA: the bottom differentials:
An easy way to think about this is that the teams with a positive differential are lucky and the teams with negative differentials have been unlucky. However, just because a team is unlucky doesn’t mean they’re good, as the Astros have the worst ERA in the league, they’re unlucky, but still have the worst xFIP in the league.
Here’s a look at the statistical breakdown of only the differential:
Three teams really stand out on the list: the Tigers, Pirates and A’s. The Pirates and A’s both have performed much better than you’d expect—in fact, the A’s and Pirates have a differential which is two standard deviations beyond the mean. Meanwhile, the Tigers ERA is much higher than how they’ve pitched, and fall nearly two standard deviations from the mean in the wrong direction (and with FIP they are more than two standard deviations; I’m not going to post the FIP info, but it’s similar as you’d expect).
Let’s take this team by team.
Pirates: The good news is that their xFIP is 8th best in the majors and their ERA is the best in the league. Their HR/FB rate is a tad below league average, but nothing that screams smoke and mirrors. The Pirates are where they are by mixing skill and luck.
First the skill. They lead the league in ground ball rate at 50.9%, this is two standard deviations beyond the league average. That’s really good. I think ground balls is more of a skill than luck, but obviously there is a bit of both involved. And in a way, it’s amazing their high ground ball rate has lead to an insanely low BABIP... the luck.
The team .265 BABIP is crazy low. Between 2009 and 2012, only the ‘11 Rays had a BABIP below .270, and only two other teams had a BABIP below .275. In other words, some sort of regression is probably going to take place, some of those ground balls are going to get through the infield for hits. That’s going to lead to more base runners. Base runners mean runs, unless...
You’re able to keep the strand rate (LOB%) high. And the Pirates lead the league in that too with a 77.7% strand rate (again two standard deviations beyond the mean). So guys aren’t getting on base, and when they do get on base they’re left there... that leads to not many runs and you get the Pirates. They’re doing this on some skill and a good amount of luck.
Odds are they can’t keep up the low BABIP and high LOB%, but I don’t doubt their ground ball rate staying high. They’re a pretty good fielding team, so that’s going to help keep runners off base. But the best news for Pittsburgh is that they’ve got 56 wins in the bank and a 5/5.5 game lead over the Nats, Phillies and Dodgers. Last year, 88 wins got the Cards into the playoffs; they don’t even need to play .500 baseball to reach 90 wins. So while they probably won’t keep playing .600 baseball, they’re a really good bet to make the playoffs.
A’s: Hey they’re pretty good. What’s interesting is their FIP-ERA spread isn’t nearly as great (0.24) which while still on the positive side, really highlights the A’s success this year: they haven’t allowed home runs.
Their 8.5% HR/FB rate is the lowest in the majors and what makes it really amazing is that they’re also last in ground ball rate at 39.2%. In other words, the A’s get a lot of outs via the fly ball and those fly balls leave the yard at a rate well below the league average/median (10.8%).
The A’s also have a pretty low BABIP (.272), and while you’d expect that to rise, it’s not as likely as the Pirates. But the A’s have their work cut out for them still as the Rangers are right behind them and then the entire AL East (minus Toronto) and the Indians are in this wild card race. So Oakland has had some luck, but really it’s the BABIP more than the home run rate, since their HR/FB has been around that 8/9% the last few seasons, probably due to where they play their home games.
Tigers: And now, on to the most overrated team in the majors. The Tigers are good, they’re really good. But the ‘27 Yankees or ‘05 White Sox they aren’t. Sure the numbers look great because they strike out everyone—9.11 per nine which leads the majors and is two standard deviations beyond the mean. They’ve got a slight above average ground ball rate and a slightly below average LOB%. They don’t allow a ton of home runs per 9, but their HR/FB rate is right around the league average.
Yet, their FIP and xFIP spreads are huge. Like only Seattle has sort of as large of a spread as the Tigers. Many will say that the Tigers are unlucky with a BABIP of .312 which is tied for worst in the majors. But I disagree.
What were the Tigers expecting when they trot out Miggy, Prince and Peralta every day? Miggy’s -11.9 UZR* is brutal and Prince’s -7.7 is barely better and rank last and second to last in the league at their position. Peralta, who came over from Cleveland with bad defensive figures was solid last year by UZR, but I wonder if that might have been because he was getting to a few balls that a ‘normal’ shortstop wouldn’t get because the third baseman would have taken care of it. This year his UZR numbers are outright average which leads me to believe that if you hit a ground ball against the Tigers, you’ve got a good chance for it to turn into a single.
*Like everyone I don't put much stock in single season UZR, but these two have never been all that great in the field and they fail the eye test too.
And that’s how you beat the Tigers. You put the ball in play. The Tigers power arms will expose high strikeout teams more so than anyone else in the league. But teams that don’t strike out as much are Detroits achilles heel because the Tigers can’t field.
I think the Tigers are too good and have too many games against the Sox to not make the playoffs. But they should be worried because I’m not sure that BABIP is going to regress. But you know what might regress? The Indians HR/FB rate of 12.9%, tied for highest in the majors (and don't forget, the Tribe make an appearance in the worst xFIP-ERA spread). If the Indians pitching staff can stop walking everyone and then get some fly ball luck, the Tigers might find themselves in a one game playoff against the Rangers or O’s or Yankees. Or out of the playoff picture entirely.
Of course, if I was the Tigers, I'd sacrifice Peralta’s offense for a slick fielding shortstop. Last year, they upgraded their defense at second when they picked up Omar Infante. I think the smart move would be to sacrifice whatever offense Peralta is giving you for a shortstop that can cover for Miggy’s horribleness at third, because it will matter in the playoffs.