Joe Kelly and the Trap of ERA

Tonight, the Cardinals and Dodgers square off in Game 1 of the NLCS. The Dodgers are throwing Zack Greinke, who you probably know as one of the best pitchers alive. The Cardinals are throwing Joe Kelly, who, if you don’t watch the Cardinals regularly, you may have never heard of. But, being the Cardinals, it is no huge surprise that they have found some moderate prospect in the third round and turned him into an ace. This is what they do. So, Joe Kelly and his 3.08 career ERA is taking the mound for the Cardinals tonight as yet another example of the Cardinals ridiculous player development success.

Except Joe Kelly is a little different than the rest of the terrific young arms the Cardinals keep pulling out of thin air. A table of the most often used 27-and-under pitchers that St. Louis has thrown over the last two years, to illustrate the difference:

Name	IP	BB%	K%	HR/9	BABIP	LOB%	GB%	HR/FB	ERA	FIP	xFIP	WAR	RA9-WAR
Lance Lynn	377	9%	24%	0.71	0.317	74%	43%	9%	3.88	3.38	3.63	6.0	4.4
Joe Kelly	231	8%	16%	0.78	0.297	78%	51%	10%	3.08	4.00	4.12	1.2	3.5
Shelby Miller	187	8%	24%	0.96	0.280	81%	39%	9%	2.94	3.54	3.70	2.5	3.8
Jaime Garcia	177	6%	19%	0.66	0.327	70%	57%	10%	3.81	3.20	3.36	3.2	1.6
Trevor Rosenthal	98	7%	33%	0.55	0.313	77%	47%	8%	2.66	2.18	2.52	2.4	1.6
Michael Wacha	64	7%	25%	0.70	0.275	80%	44%	7%	2.78	2.92	3.36	1.1	1.6

By innings pitched, Kelly ranks second only to Lynn in terms of young pitcher workload for the Cardinals since he was called up last year. And over the course of essentially one full season’s worth of pitching, Kelly’s results have been excellent, as his +3.5 RA9-WAR show. But, note how he got there.

Kelly has the lowest strikeout rate of the group, by a good margin, and has the second highest walk rate. While pretty much every other young Cardinals hurler has dominated the strike zone, Kelly has thrown 231 innings as a pitch-to-contact groundball guy, only he hasn’t really limited walks the way you want a pitch-to-contact groundball guy to do. In terms of generating walks, strikeouts, and ground balls, Kelly has been pretty ordinary.

But that ERA isn’t ordinary, and so now is usually the part of the post where we try to talk about how Kelly has either limited his home runs on fly balls or the amount of hits he allows on balls in play. Except Kelly doesn’t really do either of those things either. His .297 BABIP and 10% HR/FB rates are almost exactly league average, and don’t really explain any of the variance between his excellent ERA and his mediocre FIP and xFIP.

Instead, we come back to sequencing. It’s the 2013 Cardinals, so of course we do. Based on the quantity of individual events Kelly has allowed, he hasn’t really been that great as a big league pitcher. Based on the order in which those events occurred, though, his results have turned out strongly in his favor. Here’s how this has worked over his career.

Split	IP	BB%	K%	HR/9	BABIP	FIP	xFIP	AVG	OBP	SLG	wOBA
Bases Empty	119	10%	15%	0.53	0.315	3.81	4.35	0.271	0.344	0.380	0.323
Men on Base	111	6%	16%	1.05	0.275	4.21	3.87	0.251	0.312	0.393	0.305
Men In Scoring	61	8%	17%	0.74	0.224	3.97	4.01	0.200	0.280	0.296	0.250

Basically, Kelly’s .297 BABIP allowed is skewed heavily towards bases empty situations. With runners on base, his BABIP has been a little below the average, and with runners in scoring position, it’s been absurdly low. And if you’re not giving up hits with men in scoring position, you won’t give up many runs either. This has basically been Kelly’s recipe for success in the big leagues: put them on and then leave them there.

Of all the ways to run a low ERA, this is probably the least sustainable. Some pitchers can hold down hits on balls in play, and some pitchers can hold down their home run rate even while giving up a lot of fly balls, but there simply isn’t the same observed population of pitchers who can consistently get into and out of jams on a regular basis. Good pitchers don’t allow baserunners, basically. They don’t all do it the same way, but in general, the pitchers succeed by holding down wOBA, not by redistributing their outs to the situations that matter the most.

Over the last two seasons, Kelly is one of 135 pitchers to throw at least 200 innings. In terms of R/9, he ranks 23rd, right in between Hiroki Kuroda and Cole Hamels. In terms of wOBA allowed, he ranks 62nd, tied with Ricky Nolasco and Bronson Arroyo. The correlation between wOBA allowed and RA9 is 0.9, even in a sample of just a couple hundred innings for each pitcher. Even with all the noise, it is quite clear that wOBA allowed drives runs allowed, and that pitchers can’t really sustain results that different from their expected runs based on wOBA by very much.

While Kelly’s ERA would tell us he’s one of the Cardinals terrific young arms, he’s pitched more like a back-end innings eater than any kind of future ace. He’s not a bad pitcher, but he’s not Michael Wacha, Shelby Miller, Lance Lynn, or Jaime Garcia. He’s Kyle Lohse with more walks, at least in terms of statistical profile. The Cardinals have long had success with guys like Lohse, and he may very well shut down the Dodgers tonight, but it should be pretty clear that Kelly is the team’s worst starting pitcher, even with his particularly shiny ERA thus far.

The gap between Kelly and Shelby Miller isn’t so large that this is clearly the wrong call, especially with the way Miller’s strikeout rate sunk in September, indicating that he might just be out of gas after a long season. But with Miller available out of the bullpen and better starters to come in the next few games, Kelly shouldn’t have a very long leash. The Cardinals shouldn’t get trapped into thinking they’re throwing a 3.08 ERA starter tonight. He’s not that good, and they shouldn’t be afraid to replace him with better pitchers to keep the game close.