Do the St. Louis Cardinals have a starting pitching depth problem?

You may have heard that the St. Louis Cardinals have a few question marks in their starting rotation. First and foremost, there's Adam Wainwright's throwing elbow, which required some surgical upkeep during the offseason. Michael Wacha was diagnosed with a rare shoulder condition last year and never returned to form afterwards. Carlos Martinez has never thrown more than 108 innings in a season. John Lackey required Tommy John surgery to replace his ulnar collateral ligament a few years back. The only starter currently penciled into the rotation without at least a hint of workload or health concerns is Lance Lynn (knock on wood).

This is nothing new in baseball. Pitchers get injured at pretty high rates because the human body is not designed to throw a ball thousands of times, over and over, each year. It's a given that pitchers will sustain injuries in the season to come and that clubs will have to turn elsewhere for starts and innings.

As Jeff Sullivan has explored at Fangraphs, the five-man rotation is likely a myth. Anecdotally, the Cardinals of recent vintage support this idea. Last year, the Cardinals had 12 pitchers make at least one start and ten make five starts or more. In 2013, ten Cardinals pitchers notched a start; eight made at least eight starts. In 2012, those numbers were eight and six. So the Cardinals are going to need at least six starters and probably as many as eight.

One of the keys to the Cardinals' success these last few years has been the organization's development of in-house replacements that can step in when a pitcher goes down. Over the weekend, we looked at the remarkable change in approach for the Cardinals in this area since chairman Bill DeWitt Jr. fired Walt Jocketty and replaced him with John Mozeliak as general manager. St. Louis is leaning on homegrown pitching like it hasn't done in at least two decades.

Of course, it's one thing to throw youngsters into the fire and another entirely to experience success with it. The concept of replacement level is the foundation of the Win Above Replacement stat. As Russell Carleton wrote at Baseball Prospectus:

Replacement level is a mathematical abstraction in that no such "replacement player" actually exists—you can’t point to Larry over there and say that he is the gold standard of replacement level. But really, a replacement player is just the per plate appearance (or per inning) mathematical (weighted) average performance of all backup center fielders, multiplied by the number of plate appearances (or innings) that Trout (or any other player whose value we want to assess) played.

In using this composite sketch of the state of backups in MLB, we trade the ability to answer the question, "What really would have happened to the Angels if Trout had vanished into thin air?" for the ability to compare everyone in MLB against a common baseline.

Mozeliak and his lieutenants' establishment of a pipeline of cheap, cost-controlled pitching has taken the common replacement-level baseline for starting pitching and redefined it upward for the Cardinals.

In 2013, the Cardinals' opening-day rotation consisted of Wainwright, Lynn, Jaime Garcia, Jake Westbrook, and Shelby Miller. As discussed above, St. Louis needed more starts and innings than those five were able to provide physically. So they turned to replacement starters Joe Kelly, Michael Wacha, Carlos Martinez, John Gast, and Tyler Lyons. Combined, those five pitchers made 36 starts and notched 201 innings while posting a 3.45 ERA and 3.87 FIP. Combined, they were worth 1.7 fWAR.

Last year, the Cards called on seven pitchers who were not in the club's opening-day rotation to make at least one start. For purposes of this post, we'll exclude trade acquisitions Justin Masterson (-0.4 fWAR as a Cardinal) and Lackey (0.4). Garcia (0.3), Martinez (0.4), Marco Gonzales (0.2), Tyler Lyons (0.1), and Nick Greenwood (0.1) combined for a 4.62 ERA and a 3.91 FIP over 126 2/3 innings, which was a collective performance that generated 1.1 fWAR. Not as great or even as good as the 2013 group of St. Louis replacements, but better than replacement level. They helped keep the team afloat until reinforcements could be acquired.

So how does the replacement corps look for the 2015 Cardinals? According to ZiPS, pretty good. Before looking at the chart, though, please review the ZiPS disclaimer:

ZiPS projections are computer-based projections of performance. Performances have not been allocated to predicted playing time in the majors — many of the players listed above are unlikely to play in the majors at all in 2014. ZiPS is projecting equivalent production — a .240 ZiPS projection may end up being .280 in AAA or .300 in AA, for example. Whether or not a player will play is one of many non-statistical factors one has to take into account when predicting the future.

2015 ZiPS Projections: Replacement Starters

Given the ZiPS disclaimer, why are we looking at these stats? Not for their black-and-white stats, but for an idea of how ZiPS forecasts these players performing in the majors if they make it in 2015. These numbers tell us that, even after trading Kelly and Miller last calendar year and promoting Martinez to the rotation and perhaps Gonzales to the MLB bullpen, the Cardinals still have enough starting pitching in reserve to help them stay afloat if the rotation is hit by injuries yet again.