Andrew Miller is Scuffling, and Also Great

Here’s a sentence that I didn’t think I’d be writing in 2019: Andrew Miller has accumulated -0.2 WAR this season. By FanGraphs’ version of WAR, he’s been less valuable than a replacement-level reliever. Here’s another sentence that makes a little more sense, but is at odds with the one I just wrote: Andrew Miller might be the Cardinals’ best reliever. Now, reliever performance is volatile and all, but we’re going to need an explanation. How can those two things be true at once?

Let’s start with Miller being below replacement level, because that would have been a surprising assertion before the year. Andrew Miller has faced 139 batters this season. He’s allowed eight home runs. 6% of his plate appearances have ended with the opposing batter trotting around the bases. That surely already sounds like a ton — indeed, Miller is second in the majors in home runs allowed per nine innings, behind only Josh Osich. You don’t need a sabermetric writer to tell you that’s bad.

As bad as 2.2 home runs per nine innings sounds, though, it might be underselling how wild Miller’s season has been on the home run front. Josh Osich is a great example of the kind of pitcher who normally leads the league in home runs allowed per nine. He’s a pitch-to-contact depth reliever who works by letting opponents put the ball in play and counting on his defense to make plays behind him. Now, that strategy mostly hasn’t worked — Osich has a career ERA of 5.11, and his FIP is 5.31, so it’s not as though he’s just been getting unlucky. Still, while Osich is homer-prone, he’s mostly just contact-prone, with the home runs a cost of doing business. Strike out only 19% of the batters you face, and there will be plenty of opportunities to give up home runs.

Andrew Miller’s case of the dingers isn’t like that at all. Miller is actually one of the least contact-prone pitchers in all of baseball this year. Only 51% of the batters he has faced have put the ball in play. That severely limits the opportunities they have to hit home runs. Osich, for comparison’s sake, has let 75% of batters put the ball in play. Miller is giving up home runs at a truly alarming rate considering how few opportunities he gives batters to put a ball in play.

Look instead at home runs per batted ball, and Miller’s performance stands out. Here are the top five pitchers this year when it comes to home runs allowed per batted ball:

Josh Hader is a unicorn, and also the most extreme fly ball pitcher in baseball. The rest of the list is a who’s who of pitchers on roster peripheries. Dan Straily put up 9-handles for his ERA and FIP before being sent to Triple-A by the Orioles. Cody Allen was outright cut by the pitching-needy Angels — he’s currently toiling in Triple-A Rochester with a 9.14 FIP. Corbin Burnes lost his spot in the Brewers’ starting rotation, then got demoted to the minors, then got injured. They’re a motley crew, these high-homer pitchers.

Even Hader isn’t a good comparison for Miller. When opponents put the ball in play against Hader, it’s basically always in the air. His 0.36 GB/FB ratio is the lowest in baseball. He’s not even allowing all that many home runs per fly ball (roughly 20%). He’s simply allowing fly balls for all of his contact. That leads to a high home run total, but it also lowers his BABIP — fly balls that don’t become home runs very rarely drop for hits. His .185 BABIP is among the best in the major leagues, and his xBABIP isn’t far behind at .239.

Andrew Miller isn’t much of a fly ball pitcher. His GB/FB ratio of 1.04 is barely lower than the league average of 1.21. He’s rocking a .302 BABIP, hardly exceptional in either direction. The point is, he’s not giving up his home runs through fly ball volume — literally a third of the fly balls hit against him have gone for homers, the highest rate in the majors among pitchers with 20 innings pitched. When batters put the ball in the air against Miller, they’re producing a .596 wOBA this year, nearly 100 points higher than the league average. Not exactly what you’d like to see from your relief ace.

Well, we have the “why does Andrew Miller have negative WAR?” question sorted. It’s the home runs! It’s not easy to have a 5.15 FIP and a 3.41 xFIP, but Miller has managed it. Let’s move to the second statement I made. Is Andrew Miller really the best reliever on the Cardinals, playoff hopefuls who sport the highest bullpen strikeout rate in the game? Can a team’s best reliever still have negative WAR halfway through July?

Allow me to convince you. First, consider this: Miller is striking out 35.3% of the batters he faces this year. That’s not the highest rate of his career, but that’s only because he was the best reliever in baseball a few years ago. It’s still tied with Aroldis Chapman for the 15th-best rate among relievers, and the second-best rate on the Cardinals behind Giovanny Gallegos. Only six of the bullpen arms ahead of him run higher groundball rates than Miller does, and mixing grounders with strikeouts is the gold standard among relievers.

As good as Miller’s season-long strikeout numbers are, though, they’re underplaying his recent form. Take a look at his strikeout and walk rates by month, and you’ll start to see what I mean:

Early in the year, Andrew Miller had a problem. He couldn’t locate his slider for a strike. When I say couldn’t locate, I’m not kidding — he was hitting the strike zone on 35% of his sliders, by far a career low, and batters didn’t chase enough to make that work. His command was spotty overall, not just with his slider — when he got to three-ball counts, he was only getting pitches over the plate 44% of the time, a bottom-ten rate in baseball. Batters were content to take their walks, and Miller had no counter. He continued to go to his slider, even in three-ball counts, and batters took it and walked. More than a third of his three-ball pitches were ending in free passes , well above the league average of 24.6%. In short, his command was holding him back.

Since the beginning of May, Miller seems to have worked himself back into strike-throwing form. He throws his slider for a strike 47% of the time. With three balls, he’s gone from one of the worst pitchers in baseball at getting the ball over the plate to slightly better than average. He’s walking opposing hitters on 24.6% of three-ball pitches, right in line with league average. Essentially, he’s turned his biggest weakness — and make no mistake, Miller’s command was enough of a weakness that he was running a gruesome 8.16 FIP (and 5.49 xFIP) — into an unremarkable part of his game.

And when his control isn’t holding him back, he’s well-nigh unhittable. That sweeping, are-we-confident-physics-is-currently-working slider he’s known for still baffles hitters. His 14.1% swinging strike rate is stellar, and he gets misses on 32% of opposing batters’ swings, a top-20 rate in baseball. With his pesky control problems out of the way, his strikeout rate is 39.8% since May 1, his walk rate a minuscule 6%. The home run problems haven’t gone away (30.8% HR/FB), but even with those, he’s pitched to a 3.55 FIP (2.31 xFIP). By K-BB, he’s among the very best pitchers in the game:

Remember earlier in the article when I mentioned that Miller was allowing an abysmal .596 wOBA on balls hit in the air? That was a bit of a diversion. Those might be the observed results, but Miller has been unlucky given the contact he’s allowed. His xwOBA is a still-not-amazing .519, which is a smidgen higher than the league average .508 wOBA allowed on balls hit in the air this year. That 80 point gap, though, reflects how unlucky Miller has been to have so many of his fly balls leave the park.

The point of all of this is that Miller, right now, is one of the most fearsome relievers in the game. He’ll probably strike you out, and if he doesn’t, he gets groundballs well enough. Platoon split? There’s basically none to speak of — he’s allowed a .312 wOBA to righties in his career, .298 to lefties. If you manage to hit the ball in the air, that’s good — but even there, he’s allowing a quality of contact that clocks in right around league average.

At the same time, though, he legitimately has been below replacement level this year. He’s giving out home runs like party favors, and you can’t afford to be homer-prone in 2019 if you want to be a successful pitcher. You can strike out all the batters you want, and walk as few as you want — give up home runs, and you still won’t run an elite FIP. There’s nothing fake about that.

So what do we make of Miller overall? Is he one of the best relievers in baseball, or performing about the same as a minor leaguer would in the same position? I would argue that he’s both. Put Andrew Miller on a mound, tomorrow, and there aren’t many pitchers I’d take over him. At the same time, though, sometimes you can run out a great reliever and get a 30 inning stretch of garbage results.

All of us know, I think, to look at reliever ERA’s with a healthy dose of skepticism. Edwin Diaz isn’t a 5-ERA true talent reliever, regardless of what his numbers are this year. Miller, though, shows that we should probably be careful about looking at FIP, even with more than half of a season in the books. Statistics, even the best-intentioned and most context-neutral statistics, can mislead. Relievers operate in a world of minuscule samples, a world where a single home run can be the difference between a good and bad month.

That Andrew Miller has been bad is an objective fact, and it’s also not particularly useful when you’re trying to figure out what he’ll do tomorrow. That Andrew Miller is great is something that I can only infer from a few statistics, but it’s every bit as relevant to what he’ll do tomorrow as his 2019 results. Baseball is weird and frustrating that way, and relievers particularly so.

That’s the nature of all relievers, of course. But it’s more viscerally interesting in the extremes — when a pitcher is worse than replacement level by results and excellent by other measures. Cardinals fans are likely frustrated that their team’s big offseason pitching signing has been as useful to the team as a minor leaguer on the Triple-A shuttle. It’s hard to square that in your head with the fact that in Miller’s next outing, he’s pretty likely to be great, and I get that. Doesn’t make it any less true, though.