The Importance of Starting Pitching Depth

Everybody knows that a good team needs depth, especially when it comes to pitching. The underlying questions are: how much depth is necessary, and how important is this depth to a team’s overall success?

The Cardinals have long been heralded as a team that has great in-house pitching depth. Seemingly whenever a starter goes down, there is a man who steps up and performs admirably. Players such as Luke Weaver, Austin Gomber, and Daniel Ponce de Leon have demonstrated this in recent years. When players come up from Triple-A and give strong performances out of the rotation, this helps soothe the sting of injuries. And it’s no coincidence these same teams are often in postseason contention.

During the 2019 MLB season, the average team used a total of 12.9 starting pitchers. Subtract that by five (the typical rotation size) to get an average of 7.9 ‘depth’ starters (we’ll call it eight for convenience). These eight extra pitchers started an average of 39.27 games. So, this means that the average team needed nearly two-and-a-half starting rotations over the course of the season. This also means that nearly a quarter of all starts came from pitchers that were not among the top five starters (in terms of starts) on the team.

In order to find these numbers, I counted how many pitchers recorded at least one start and subtracted the top five pitchers, in terms of games started. With the pitchers left over, I tallied how many combined starts they made. I did this for every team in the league and then averaged them together. I understand that this is relatively basic and overstates the numbers a little bit because I did not factor out games that were started by an opener or bullpen games. However, this should not throw the numbers off by too much, and a lot of times bullpen games happen when the starting rotation is injured or fatigued. So these numbers are probably a little rough, but they are accurate enough to guide this story.

The St. Louis Cardinals were among the healthiest teams in the league in 2019. Obviously Alex Reyes remained injured and Carlos Martinez had to move to the bullpen, but besides those two, the Cardinals used just two ‘depth’ starters (Daniel Ponce de Leon, and Genesis Cabrera) to cover just 10 starts. Both of these figures were the lowest in baseball. The team had extraordinary health among its top five starters, and that was an undeniably huge asset. For the most part, this has been an asset for the Cardinals for the last decade. In fact, the Cardinals have not used more than six ‘depth’ starters since 2014. Some of the Cardinals consistent year-to-year success can be attributed to strong pitching; beyond that, its strong pitching depth and good health.

It would make sense that good health would be a common trait of good teams, and that idea is supported by the numbers. Playoff teams only used an average of 6.5 ‘depth’ starters in 2019, and these pitchers made an average of 31.6 starts. This is a good amount less than the average of 8.6 ‘depth’ starters making 43.1 starts among teams that did not make the playoffs.

From these numbers it is clear that health, first and foremost, is strongly correlated with team success. However, it is also clear that talented depth options are also necessary for a team that has playoff aspirations. Nearly eight extra starting pitchers were needed to cover over 39 starts per team this season. This is a significant amount of depth that is required for the typical team. A lack of solid depth options could have a significant impact on a team’s season as nearly a quarter of the average team’s games were started by a pitcher that was not in the five man rotation. Obviously, the percentage is not that high for the average playoff team, but the percentage (19.5 percent) is still significant. A lack of solid, MLB-caliber depth options could cost the average team a couple of wins — and as we know, that could make all the difference in a team’s playoff chances.

While the Cardinals had extraordinarily good health in 2019 (at least among the pitching staff), this cannot be relied on every season. With Michael Wacha likely leaving the team in free agency, the Cardinals will have four returning members of the rotation (Flaherty, Mikolas, Hudson, Wainwright). This leaves one open rotation spot for next season; however, it is difficult to expect similar contributions in 2020 from Waino (38-years-old) and Hudson (4.93 FIP/4.55 xFIP) that they gave this year. This means there is likely to be even more starts up for grabs than usual.

Barring any future starting pitcher acquisitions, he top contenders for depth starts (and the final rotation spot) appear to Martinez, Reyes, Ponce de Leon, Helsley, Cabrera, Jake Woodford and Austin Gomber. Other fringe options could be the emergent Tommy Parsons, who reached Memphis last year but struggled a bit in Springfield, and Alex FaGalde. This appears to be a pretty strong group at first glance, but there are plenty of question marks. At this point it seems foolish to depend on Reyes and Martinez to have the health and arm strength to pitch out of the rotation, even though it is still possible. Also, Cabrera struggled in Memphis and St. Louis last season while Woodford posted a solid ERA (4.15) in Memphis but a questionable FIP (5.54) and xFIP (6.22). Even Austin Gomber is coming off a big injury that kept him out for most of last season.

Nevertheless, it is important to keep in mind that these players are depth options because they aren't yet trusted enough for full-time roles. If they were without major question marks, they would already be pitching out of the big league rotation.

So, if the Cardinals want to be safe, then it might be smart to make some external pitching acquisitions this winter. If they decide to stay in-house, this does appear to be a pretty solid group of possible ‘depth’ starters for the St. Louis. In the end, either way, the Cardinals will hope for good health — and hope that the Memphis pitching pipeline can continue to churn out MLB quality starters.