How many starters do the Cardinals need for 2015?

The Cardinals starting five in 2015 appears nearly set with Adam Wainwright anchoring the rotation followed by Lance Lynn, John Lackey, Michael Wacha, and Carlos Martinez. The Cardinals entered 2014 with depth in the rotation with Carlos Martinez in the bullpen and Tyler Lyons in Memphis, but ended up using twelve different starters and finding it necessary to trade for Justin Masterson and John Lackey to provide innings after the All-Star break. Masterson did not provide the innings sought as the Cardinals caught the Brewers and held off the Pirates down the stretch, but having gone from a position of strength to a position of need in just a few months illustrates the fragile nature of the rotation. The Cardinals will need depth in the rotation with uncertainty in health and age (both young and old) surrounding the Cardinals' starters this year.

In the Viva El Birdos podcast earlier this week, Ben and I discussed the need for depth in the rotation and the myth of the five-man rotation. He mentioned research done by Jeff Sullivan on that topic, and I indicated it might have been Eno Sarris. As it happens, both writers from Fangraphs have done some work on the subject. First Sullivan, looking at the pitchers after a team's top five starters.

Overall, these guys made 967 combined starts, for an average of 32 per team. They threw a combined 5,097 innings, for an average of 170 per team. They totaled 7.2 RA9-WAR, and 24.1 regular WAR, for averages of 0.2 and 0.8. Their combined ERA- was 125; their combined FIP- was 119.

The pitchers after a team's top five in 2013 (in starts made, not necessarily opening five), performed poorly overall,  barely above replacement despite taking roughly a fifth of every team's starts. The Cardinals can be hopeful that their five starting pitchers take the bulk of the starts in 2015, but that rarely proves to be the case. Over the past ten seasons, the number of Cardinals starters to make at least 25 starts are in the graph below.

The Cardinals have not had five starters go a full season since 2005, the year they won 100 games. Every year since then, they have had at least one starter fail to get 25 starts and in six of the nine seasons, only 3 starters made close to a full season. Eno Sarris did some further research on starting pitching depth. Given the number of starters and starts teams lose to the disabled list, he found:

Here's what the average team (six DL stints, 360 days) will suffer:

*10% likelihood that 4+ starters will be hurt at the same time (.082+.016+.001)
*32% likelihood that 3+ starters will be hurt (0.22 for exactly 3, plus the 4+ injured pitchers above)
*65% likelihood that at least 2 starters will be hurt at any given point in the season (105 games)

...

Since 2011, the average team has seen ten different pitchers start a game for them over the course of a single season.

Note: If that quote looks familiar, it is not the first time I used it. It is also from my post before the season started on the Cardinals strategy with Carlos Martinez, writing he would likely get starts in 2014 due to attrition on the staff.

The Cardinals have ended up on both the good and bad side of that spectrum over the last decade. Here is the number of starters they have used in each season over the past ten years.

The Cardinals have averaged 9.7 starters per season over the past ten seasons, That number includes spot starts by those who failed to make an impact. Going a bit further, here is the number of starters per season the Cardinals have used that have made at least five starts in a season.

Above we see the Cardinals starters who have actually made at least a little bit of an impact. This past season was an aberration, with 10 different pitchers making at least five starts. The eight seasons prior, the number was in the 6-8 range. While last season proved a team cannot count on needing just 6-8 pitchers for a decent time during the season, the Cardinals can feel comfortable knowing that number should be able to get the job done.

Currently the Cardinals have Marco Gonzales, Tyler Lyons, and the oft-injured Jaime Garcia as potential rotation backups. They also have Tim Cooney who could fill in for a few games. Yesterday, I looked at some of the more bottom of the barrel options the Cardinals could look at in free agency as starting pitcher depth. I noted that none of the options looked particularly pleasing, but the Cardinals may add someone for depth in the spring and potentially a spot in Memphis or the bullpen in case the Cardinals need extra help.

The likelihood of attrition is the reason the Cardinals could bring someone who appears to have little value to the Cardinals at the moment. The Cardinals have little interest in blocking Carlos Martinez, but a team cannot have too much pitching depth. Every team will go to a sixth starter at some point, likely a seventh, eighth, ninth, and tenth. The Cardinals are wise to hold on to the depth they have and to bring as much extra help as they can get. The season is long, and the more pitching the Cardinals have, the better positioned they will be to weather a storm of injuries and ineffectiveness that is almost inevitable with a modern rotation.