The sustainability of the St. Louis Cardinals' starting pitching

The St. Louis Cardinals' starting rotation has been excellent so far this season, doing far better than anyone probably could have expected after the loss of Adam Wainwright. Going into Friday night, the Cardinals' rotation led the league in ERA (3.06) and fWAR (6.6), was second in FIP (3.31), and sixth in xFIP (3.47). The Cardinals' rotation is one of the main reasons why the team has the best record in baseball, and with the losses of Matt Adams and Matt Holliday, the team may have to rely on their pitching more than ever going forward.

Given how good the Cardinals' rotation has been this year, it makes sense to wonder how sustainable this performance really is. As Bernie Miklasz pointed out about a week ago, Mike Matheny is not a fan of the word "unsustainable" when describing the Cardinals' rotation.

"They’ve done it this far," [Matheny] said, "so why can’t it be sustainable? I get it, there’s a lot of numbers that support it would be hard to. But I don’t want them even glimpsing at that. It’s not like we’re pulling numbers out of the sky and saying, ‘If you could only do this.’ They’re doing it."

Matheny is right that the Cardinals have maintained this performance for over two months now, which is not an insignificant sample size. At the same time, further analysis is still needed before we can comfortably say that the Cardinals' starters have a good chance of pitching like this for the rest of the season. After all, VEB readers are not prone to assume that Mike Matheny's gut-feeling optimism about matters such as these has any basis in reality.

With that being said, I thought I'd look at each of the Cardinals'' starters to see what they've done so far this year and explore whether their stats suggest that they can continue this performance going forward.

(Note: I am writing this Friday morning, so this post will not reflect any stats from Jaime Garcia's start tonight. In addition, I am aware that we are supposed to hear an update on Lance Lynn's forearm issue today, so please don't think I'm being ignorant if something bad happens and I don't mention it in my article.)

Lance Lynn

Lance Lynn is having another fine season for the Cardinals, perhaps his best to date. His strikeout rate, walk rate, and FIP are career bests (excluding his brief 2011 stint in the bullpen), and he is on pace to have his best season by fWAR. His peripherals suggest that his current level of performance is probably sustainable, assuming he stays healthy (which is an open question at this point.) Lynn's FIP is actually better than his ERA, in large part due to his above average BABIP, and while his xFIP is not quite as impressive, it should not be a huge area of concern. Lynn has consistently put up a below average HR/FB rate in his career (7.8%), a number probably aided by the home run suppressing environment of Busch Stadium.

John Lackey

Lackey has been about as good as advertised so far this year. His start on Monday bumped his ERA from 2.93 to 3.74, but he still has solid peripherals and has given the team a lot of innings this season. Lackey's performance may not be entirely sustainable due to his low HR/FB rate, but he still has plenty of value, even if he regresses a little bit. ZiPS has him projected for a 3.63 ERA and 1.7 fWAR in 114 innings for the rest of the season.

Michael Wacha

Michael Wacha's season has been eerily similar to John Lackey's with one important exception: ERA. Wacha and Lackey have a nearly identical strikeout rate, walk rate, FIP, and fWAR, but Wacha has outperformed his FIP by a full run so far this season, in large part due to a low BABIP and high strand rate. The good news is that Wacha is bringing his strikeout rate up after it was alarmingly low for much of the season. Since May 14th, Wacha has a strikeout rate of 24.1 percent and a FIP of 3.34, which is closer to what we expected from Wacha coming into the season. Going forward, Wacha won't be able to sustain an ERA in the mid 2's, but his recent performance suggests that he might not regress as much as we had initially feared.

Carlos Martinez

Carlos Martinez has had an outstanding start to the season, making major improvements after his brief stint in the rotation last year. He is using his changeup more often, striking out more batters, and going deeper into games, averaging more than six innings per start. He may be a candidate for regression due to his high strand rate (5th highest in all of baseball) and slightly below average BABIP. At the same time, his xFIP is still very good due to an extremely high HR/FB rate. What we may see with Martinez going forward is two types of regression that ultimately cancel each other out: a lower strand rate and a lower HR/FB rate.

Jaime Garcia

Jaime Garcia has been nothing short of outstanding in his first four starts this season. (I risk looking like an idiot by typing this before his Friday start against the Royals.) Yes, I am only looking at four starts here, but so far, there has been little that stands out as unsustainable. His BABIP will probably go up over the course of the season, but like Martinez, Garcia has an above average HR/FB rate, which probably won't continue either. The most encouraging things we've seen from Garcia are his low walk rate (he hasn't walked anyone since his first start), his high innings total (three starts of seven innings and one of six) and his high ground ball rate (64.5%).

Given all the injuries that Garcia has gone through to get to this point, I don't think he has gotten enough credit for what he's done in his first four starts back. Yes, his injury history makes it unlikely that he gets through the season unscathed, and any pitch he throws might be his last, but it would be unfair to say that Garcia's first four starts have been a fluke. Given the fact that most of us saw any contribution from Garcia this season as a bonus, we should be thrilled by the fact that he has given the team four starts with a high number of innings and good run prevention, all backed up by good peripherals. It would be foolish to count on Garcia to be a major contributor going forward, but we should enjoy his run of success while it lasts.

Overall, it seems as though Michael Wacha is the only Cardinals starter whose performance thus far is unsustainable, and even in his case, an argument can be made that he won't regress too much, especially if we believe he can maintain his recent uptick in strikeouts. While other Cardinal starters have some individual numbers that are unsustainable, they shouldn't have a major impact on their overall performance. In the case of Lynn and Lackey, the amount of regression we can expect isn't all that much. For Martinez and Garcia, the regression working against them going forward (due to strand rate and BABIP) has a good chance of being canceled out by regression working in their favor (HR/FB rate).

The biggest concern about the rotation going forward has to be about health and innings limits. Garcia will always be a question mark, and Lynn has been more fragile than usual this season. The Cardinals will also look to protect the arms of Wacha and Martinez, even if they haven't given either pitcher a set innings limit. For these reasons, the Cardinals will almost certainly be looking to add a starting pitcher at the trade deadline. Even so, if the performance of the Cardinals' rotation suffers for the remainder of the season, it is more likely to be due to the performance of other starting pitchers filling in (i.e. Gonzales, Cooney, Lyons), not because of the current five starters regressing in a major way.