Chris Tillman, the Orioles, and Rotation Depth

Chris Tillman has some aches in his shoulder, has recently received a shot, and may miss some time early in the season. That’s what’s been reported, at least. It might not be a big deal, considering that teams can skip a fifth starter’s spot in April and fudge their way through the month. It might be a big deal, though, once you consider the Orioles’ rotation depth relative to the rest of the league.

A couple of years ago, Jeff Sullivan and I got into studying team depth for a bit. I looked at whether teams with good depth outperformed teams with worse depth, then Jeff Sullivan looked at starting pitching and depth. Then I looked at it again. For the purposes of this post, here are the relevant findings from those pieces:

• Teams get 32 starts from starters below the top five on their depth chart.
• Teams get six starts from an eighth starter on average.
• Teams use 10 starters on average.

So, to evaluate this year’s rotation depths, I ignored the innings given to the sixth, seventh, and eighth starters on our depth charts. Those may be good approximations for this year’s personnel given our estimations of general health, but I’m dealing in averages.

We know that, in the average year, an eighth starter gets about 35 innings. That leaves 150 innings for the sixth and seventh guys. To estimate how those innings might be allocated, I went with a 2.6/1.6/1.0 weighting for the sixth, seventh, and eighth guys. That gives them 90, 57, and 35 innings, respectively, which seems about right.

To see what that might mean for the league, I took the sixth, seventh, and eighth guys on each club’s depth chart and rendered their projections into a per-inning figure. Then I re-ran them according to the weights cited above. Below are the results of those calculations — the league’s re-weighted rotations judged by the strength of their sixth, seventh and eighth starters, were they given the playing time that our empirically derived weights suggest they’ll get.

First, a few problems with this methodology. One, the Cardinals and Nationals don’t have eighth starters on our depth charts currently. I gave them a zero-win guy there, but when it came to strikeouts and walks, I didn’t know what to do. So I gave them league-average numbers. Those two teams may be overrated if you’re judging them by strikeouts and walks per nine.

Two, you can quibble with the use of the FIP-based WAR here. It’s a blunt instrument when it comes to pitching. If you want to leave home runs out of it, and go by strikeouts minus walks, though, the difference isn’t stark. The Dodgers are first, with the Astros, Pirates, and now Cardinals at the top (despite the lack of an eighth starter on our depth charts). The Padres, Marlins, and Orioles are at the bottom.

Three, this experiment still relies on our depth charts to get the guys ranked six through nine right. There will be some movement up and down — and I even added some subjectivity to the exercise by counting Brandon McCarthy as the sixth starter in Los Angeles because Julio Urias was projected for more innings by our depth chart. So you can understand that there’s a great deal of subjectivity and interconnectedness here.

You can also understand why the Dodgers do so well in our projections but seem less amazing when playing the “Who’s in the rotation now?” game. At the moment, there’s definite group of three and then Urias and then a group of other guys — but almost all those other guys have something real to offer. From McCarthy to Alex Wood and Brock Stewart, there really isn’t a team that boasts as much depth. They might get three wins from a starter who isn’t even a member of the Opening Day rotation! And from what we know about rotations, that’s an important facet of the average major-league season.

You can spot a few teams that don’t have the most amazing front five but have combated that problem with quantity. The Pirates, Astros, Rockies, Twins, and Rays don’t boast an ace’s ace maybe, or the kind of front five you’ll find in Cleveland or Queens. But they do have some interesting arms in their minor leagues, some good veteran depth, and generally deep squads.

On the other side are a few decent rotations that are on shaky ground. The Red Sox, for example, have some amazing starters at the front of their rotation. Then they have a knuckleballer and two unproven young guys if something goes wrong.

It also serves as a sobering look at depth for Baltimore, in particular. With Tyler Wilson and Mike Wright as the sixth and seventh starters, they have to hope that Chris Tillman’s shoulder is already on the mend.