Revisiting the Myth of the Five-Man Rotation

The other day, Eno wrote something up about the importance of team depth, and about the importance of being able to measure it. I think the thing I like most about the A’s roster right now is how it’s so deep in so many places. The Cardinals, too, have given themselves some flexibility. Depth is something you never think about at first — at first, you’re simply focused on the top bits of the depth chart — but for as much as the need for particular depth is unpredictable, odds are those extra players are going to matter. Players who aren’t on the opening-day roster, or who aren’t starters, are going to end up responsible for attempted runs scored and attempted runs prevented.

I think most people have a good understanding that it matters to have starting-pitcher depth beyond the front five. At least, most people who hang around at places like FanGraphs. We all get that pitchers are volatile, and we all get that pitchers get injured. Yet still there’s a focus on just the first five, because no pitcher is individually super likely to break down, and if the five are good enough you should never need a replacement, right? People talk about filling out five-man rotations, but really, a team would be fortunate to lean on a five-man rotation, and I thought it could be useful to provide some updated numbers from the season most recently finished. Those sixth and seventh starters in a system — they’re going to get innings. Sometimes a lot of them.

This is a study of just one year, and it won’t establish anything new. The methodology could probably be tweaked, but as is, it worked well enough. I exported the performance of every pitcher who started at least one game in 2013. I then sorted by team and by number of starts, and then I went in and erased the numbers by each team’s top five starters, by games. This eliminated the five guys used most heavily. Remaining on the spreadsheet are the depth guys. The depth guys and, rarely, trade acquisitions. I wanted to know about usage, and I wanted to know about performance.

This doesn’t perfectly capture the importance of depth. It might even underrate it — at times, a guy counted on from the get-go didn’t end up in a team’s top five. Which means that a depth guy ended up in the top five. With the Phillies, for example, Roy Halladay was supposed to be a dependable starter all year, but he wound up sixth on the team in starts. With the Pirates, Wandy Rodriguez wound up sixth. The Cardinals got just nine starts out of Jaime Garcia. I’m content, though, with the results, serving as approximations. The data gives a good idea of how important it is to have ability behind the intended five-man.

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 Tigers had an excellent rotation in large part because of the ability of their top five starters. Those five guys, though, also started 156 of the games, leaving just six for depth in the person of Jose Alvarez. The next team, alphabetically, is the Twins, and their depth guys made 48 starts. For the Rangers, 43. For the Orioles, 40. The Dodgers clearly had to lean on some replacements. The Blue Jays wound up somewhat in tatters. Contenders and non-contenders alike had to give dozens of starts to guys who didn’t so much figure to be starters in March and April.

Take that team average of 32 starts, noted above. That’s a fifth of all starts. That is, basically, its own rotation slot. To put it simply, teams got four slots out of the intended five starters, and then a bunch of other guys picked up the slack out of the remainder. The actual need for depth will vary from team to team, but there are games to be won and lost, and so it’s easy to see how this could make a significant difference.

Building rotation depth isn’t the easiest thing to plan for. With position players, you can keep quality depth pieces on the major-league bench. It doesn’t work quite that way with starters, because real good ones will get rotation jobs right away. You won’t be able to sign good starters to minor-league contracts to stash them away in Triple-A. You generally won’t be able to keep good, established starters in the bullpen. Good depth often has to come from within, in the form of younger talent. Depth is hard to build overnight, but it’s easy to deplete.

As an example, I instantly think of the Mariners. Right now, they’re looking at a rotation of Felix Hernandez, Hisashi Iwakuma, Taijuan Walker, James Paxton, and Erasmo Ramirez. There’s not much of anything behind them. The Mariners intend to add another starter, be it Masahiro Tanaka or a free agent or a trade acquisition. That would push Ramirez into the sixth-starter role. A follow-up move could be trading a young starter for some kind of bat, but then they’d be back in their current position, with depth in the persons of Blake Beavan and Brandon Maurer. Ramirez is probably superior, given his health, and he’d make for an excellent sixth-starter option. To trade from a pool of big-league-ready starters is to make your roster worse, because those starters are likely going to matter. It’s easy to just think about the five main guys, and see the others as just emergency options, but most teams do encounter emergencies, be they major or minor. The need for depth can be anticipated ahead of time, and better to have it and not need it than to (and so on).

Another example would be the Red Sox, who currently don’t seem to have a space in the rotation for Ryan Dempster. There are also prospects climbing the ladder, and Brandon Workman in the bullpen. Given Dempster’s salary and lack of a spot, he’s been the subject of countless trade discussions, but while there could be good sense in sending him packing, he could also still play a prominent role in Boston going forward, as the guy who’s next on the list. The Red Sox are going to need to give starts at some point to other guys, and so it’s not just about moving a superfluous player. Generally, a decent starter isn’t superfluous.

The tricky thing is the unpredictability. You never know when you might suddenly have a need, and you never know for how long that need might exist. As noted, it’s tough to build quality rotation depth, because good starters are always valued at a premium. But depth is still important, for all of the uncertainty. Every team employs a five-man rotation, but those rotations, in the end, will have consisted of more than five men. Depth should be preserved, not depleted, and the best teams are the teams prepared for the inevitable adversity. The absence of quality depth will usually cost a team, in one way or another.