Game 142 Preview: Alex Cobb, the Best 5th Starter in Baseball?

By Robbie Knopf

The amazing thing about the Rays rotation is how from one to five- even one to six- any pitcher could go out there and throw a shutout. Alex Cobb may be the Rays’ fifth starter, but he’s a pitcher who has come up huge for them this season and has been a big part of their success. The Rays’ rotation this year has by no means been perfect, but this current Rays rotation could very well be their most talented ever. But let’s talk about Cobb. Is he the best 5th starter in baseball?

First of all, what is a fifth starter? I’ll define it as a regular starter with the fewest innings of any regular starting pitcher on his staff with certain exceptions. Better-caliber pitchers who have been out with injuries for much of the season and pitchers that were dealt at the trade deadline are automatically excluded. I’ll also take out Mike Fiers from the Brewers considering how good he has been since getting called up and how many innings he’s averaging per start, making Marco Estrada eligible. We’ll set the minimum number of starts to qualify at 15.

When we set the parameters as much, there are not that many pitchers that qualify: 15. Here they are.

We see here and interesting group of young players and veterans with their levels of performance all over the place. They’re grouped in terms of ERA+, ERA adjusted to ballpark with 100 being average and higher being better. We see here that Ross Detwiler pulls away from the pack with Marco Estrada and Joe Kelly being the only ones above average. But these rankings shouldn’t be based just on ERA and ERA+. Let’s talk about the defense-independent stats for all these pitchers. Here’s everyone’s FIP, FIP- (like ERA+ but lower is better), xFIP, and xFIP-.

By xFIP-, we see that Cobb is the best, while Marco Estrada is  best in FIP, FIP-, and xFIP. Considering how good he has been overall, Estrada has to be considered the best 5th starter in baseball. I would rank Cobb second because of his FIP and xFIP, his outstanding 57.9% groundball rate, and if you take out two disaster starts in which he allowed 8 runs each, his ERA goes all the down to 3.32. To round out the top five, I would pick Detwiler, Drew Smyly, and Vance Worley.

Is Alex Cobb the best 5th starter in baseball? No, but he’s right there. Cobb has been incredible for the Rays almost the entire year and if he had not given them the type of quality outings that he has provided replacing the injured Jeff Niemann, the Rays would be much worse off. Hopefully Cobb can come up big for the Rays again tonight to nail down a big win versus the Orioles.