Nats’ post-season roster: The bullpen

I assume that the Nats will carry 12 pitchers on their post-season roster—the 4 starters and 8 in the bullpen. (Though there’s been some speculation about only carrying 11 pitchers and using the extra slot to carry another bench guy—presumably Kevin Frandsen—though I think that’s crazy. With the Nats’ deep lineup and Ryan Zimmerman available as a pinch hitter, there’s no way that an extra bench guy is worth more than an 8th arm in the bullpen.)

I’ll talk about the bench in my next post, but let’s talk about the bullpen now. With Tanner Roark, Drew Storen, Tyler Clippard, Matt Thornton, and Craig Stammen locks for the bullpen, and Aaron Barrett a strong candidate, the main debates are whether Ross Detwiler or Jerry Blevins should be kept as the second lefty, and whether Rafael Soriano should be kept on the post-season roster. Let’s look at Detwiler versus Blevins first.

Most writers are saying that Detwiler has the edge and Blevins is the odd man out, pointing to Detwiler’s advantage in ERA (4.11 for Detwiler compared to 5.17 for Blevins). I, of course, disagree.

• Why is Blevins a better choice than Detwiler?

Although Detwiler has the advantage in ERA, ERA is a terrible statistic for evaluating relievers. And in just about every other statistic, Blevins has the advantage:

• But hasn’t Detwiler been better than Blevins recently?

Detwiler has pitched better in the second half than he did in the first half and holds the advantage in ERA (4.71 to 5.82), but I think it would be a stretch to say that he’s pitched significantly better than Blevins over that span. Here are their statistics since the All-Star break:

Although the differences are smaller for the second half, the edge still goes to Blevins.

• So what’s wrong with ERA that it gives such a different answer?

ERA doesn’t work for relief pitchers because they often come into the game with base runners already on, whom their not “responsible” for in the calculation of ERA, and also can leave with runners on who they “are responsible for,” even though they have no control over whether those runners subsequently score.

For example, this season Blevins has come into games with 32 inherited runners and has allowed only 4 (13%) to score—a very good ratio (the Nationals team average is 28%) for which he receives no credit in his ERA. Conversely, he’s been pulled from innings with a total of 15 runners he was responsible for, and the subsequent reliever(s) allowed 8 of them to score—all charged against his ERA even though he didn’t have anything to do with it after he was pulled.

A much better statistic is RE24, which appropriately assigns each pitcher responsibility for changes in run expectation that occurred while he was on the mound. It assigns every run allowed to the pitchers who were pitching, but in proportion to their responsibility for each run. Blevins is ahead of Detwiler with an RE24 of –0.59 to –5.22 (that is, both pitchers are below average in this statistic, but Blevins is close to average whereas Detwiler is 5 runs below average).

• But isn’t Blevins hurt by his huge platoon differential?

It’s true that Blevins has one of the largest platoon differentials in baseball this season. Right-handed batters are hitting .307/.403/.436 against him, while left-handed batters are hitting only .163/.208/.224. As I pointed out in mid-July, however, Matt Williams hasn’t really been taking advantage of this differential by using him in a LOOGY role in short appearances against tough left-handed batters. In fact, Blevins has been allowed to face more righties than lefties.

Since then, things really improved. Since the all-star break, he’s continued to face more right-handers than lefties. It’s not that Williams doesn’t know how to use a LOOGY—since Thornton has come aboard, he’s been used in a LOOGY role several times and has faced more lefties than righties (even though Thornton’s platoon differential probably isn’t nearly as large as Blevins’). It just seems that Williams doesn’t trust using Blevins in any kind of high leverage situation, which, of course, is a problem if he’s selected for the post-season roster.

I think Williams failure to use Blevins in the LOOGY role that he seems suited for is a misuse of a valuable asset. In the regular season, I get that using a pitcher for one or two outs may put too great a strain on the rest of the bullpen, but in the post-season we’re going to run up against some tough left-handed hitters in high-leverage situations, and the Nats would be much better off if there are two pitchers that Williams can call on in those situations. Blevins is the right pitcher for that role. And with Roark available for long relief (Detwiler’s main role), I don’t know what Detwiler’s good for. He doesn’t get enough strikeouts to bring him in when you need one. I think he’d just be dead wood on the roster.

• Weren’t you going to say something about Rafael Soriano?

I see he pitched the ninth inning tonight and shut down the Marlins in order. He’ll probably get about three more chances to pitch before the end of the regular season, and unless he has major meltdowns in a couple of those appearances, I expect to see Soriano on the post-season roster. I suppose that Blake Treinen is another option, and he has looked good in most of his appearances with the Nats this year, but he’s basically a groundball pitcher who doesn’t get a lot of strikeouts, whereas when Soriano is pitching well, he gets a fair number of strikeouts. I’d say there’s at least a 95% chance that Soriano will be on the Nats’ post-season roster.