Rays have MLB's best ERA since using 'opener'

On May 19, Sergio Romo took the mound to be Tampa Bay's first "opener." A week later, the club traded longtime closer Alex Colome to Seattle. Since then, the injury-plagued Rays have also lost Chris Archer and Jake Faria from a staff that's already seen Brent Honeywell Jr., José De León and Anthony Banda undergo Tommy John surgery. Other than three games with Baltimore, every team they've played since then has had a winning record.
This is the perfect recipe for disaster. This is how seasons implode. It hasn't happened. Since May 19, Tampa Bay has had baseball's most productive pitching staff. That's a pretty big claim, and it's not the same thing as the best pitching staff, but the numbers tell a pretty strong story. Since that day, here's how the Rays' staff ranks.
Tampa Bay's pitching ranks since May 19
• First in ERA (2.87)
• First in opposing batting average (.205)
• First in on-base percentage (.282)
• First in slugging percentage (.338)
• First in wOBA (.271)
• First in ground ball rate (46.6 percent)
The Rays had a 4.45 ERA when they started their new strategy, eighth worst in baseball. They've shed some talented pitchers since then, yet seen their fortunes completely turn around. Based on the enormous change in performance, it's simple to say that trying something innovative that no other team had committed to before -- and that almost no one has followed in doing since -- is the reason for their success. The "opener" is behind all of this. Right? 
Not quite. If it were, 29 other teams would be doing the same thing. "The opener" is a good idea, and it matters, but what's driving this pitching performance for Tampa Bay is a little more complicated. Let's figure out why.
1. The Rays' ace is pitching like an ace
For all the focus on how the Rays are challenging the accepted roles of a pitching staff, the biggest reason for their success is coming from the most traditional source of all: a starter who is actually being used like a starter. You might think that when we say "ace," we're talking about Archer. We're not. Tampa Bay's real ace is lefty Blake Snell.

A year ago at this time, Snell was in the Minors, having been optioned down in May due to continuing inconsistency. When he returned in late June, he was a different pitcher, crediting a change in where he positioned himself on the mound. So far in 2018, Snell has legitimately been one of the best pitchers in the game, as a career-high strikeout rate (28.1 percent) and a career-low walk rate (10 percent) have helped him post a 2.31 ERA.
Snell also has the third-lowest hard-hit rate (27.4 percent) of the 121 starters who have allowed 150 batted balls. Since Tampa Bay started with "the opener," he's been all but untouchable; only Atlanta's Mike Foltynewicz (1.22) has a lower ERA than Snell (1.27). If the Rays had five Snells, they wouldn't need "the opener" at all. The one they have is pitching like one of baseball's best.
2. Tampa Bay is getting a ton more ground balls
There have been 13 pitchers to appear for the Rays both before they started "the opener" and after. That includes the big names like Snell and Archer, but also lesser-known arms like José Alvarado, Ryne Stanek (himself an "opener" six times), Ryan Yarbrough and Austin Pruitt.
For that baker's dozen of pitchers, some of the metrics haven't changed much at all. They struck out 22.7 percent of hitters through May 18, and 23.8 percent since, though that's been balanced out by the fact that after walking 8.1 percent of hitters through May 18, they're walking 9.5 percent since.
Their hard-hit rate hasn't changed (34.2 percent before, 34.7 percent since). Their on-base percentage has only dropped slightly, from .302 to .295. Even the group's BABIP hasn't changed, holding steady at .279 before and .275 since.
So what has changed? Their slugging percentage has dropped from .396 to .339, a sizable difference of 57 points, and that's in large part because a grounder rate that was below 42 percent before (ranked 23rd) has be an MLB-best 49 percent since.
Now, what's behind that may be more complicated than we can get into here, but one thing is for sure: The Rays are simply pitching differently. Taking these 13 pitchers as a group, they're throwing fewer four-seamers and more sinkers and curveballs, which is a great way to get more grounders. (Also worth noting: Only one team has allowed a lower average on fly balls in play, making for a powerful combination.)

Perhaps most notable in that group is Chaz Roe, best known for his physics-defying slider. He's doubled his sinker usage, he's added 15 points to his grounder rate -- and he's allowed one run in 15 post-"opener" games.
3. The new guys are pitching better than the old guys
It's not all the same pitchers, of course. Setting aside appearances b position players and brief cameos from Hunter Wood and Chih-Wei Hu, there were two Rays pitchers who saw time before "the opener" who haven't appeared since. Andrew Kittredge, who had a 9.72 ERA and a .410 wOBA in 16 2/3 innings, was entirely ineffective. Yonny Chirinos showed promise (3.71 ERA, .309 wOBA) in six outings, but he hasn't appeared since April 28.
Meanwhile, Tampa Bay has benefited from some outstanding performances from some brand-new and well-traveled arms. Wilmer Font is already on his third team of the season, and his results with the Rays have been stunning -- after a 11.32 ERA with the Dodgers and a 14.85 mark with the A's, he's allowed four runs in 22 innings for Tampa Bay, perhaps helped in part by the club's move to push him to the third-base side of the rubber. Vidal Nuño, who is on his fifth team in the past five years, has a 1.56 ERA in 17 1/3 innings.

Rookie Diego Castillo has a 1.46 ERA in his first 12 1/3 innings, striking out 13, while Nathan Eovaldi, who was injured on the eve of the season just shut out the Nationals over six innings. Font, Nuno, Castillo and Eovaldi all have better wOBA marks than Kittredge or Chirinos.
Has "the opener" mattered?
Those are all legitimate reasons for improvement, and few of them have anything to do with "the opener." So: Is it actually working? Or is Tampa Bay's good performance about unrelated issues?
It's a complicated question, because it's hard to evaluate. In "opener games," the Rays have had a 3.64 ERA; in games where they haven't, since May 19, they've had a 2.55 ERA. You could take that to mean that it's not working, but of course that is not the correct way to look at it, because only the non-"opener" group benefits from Snell.
Ultimately, you'd want to see if "the opener" games featured better platoon advantages and fewer times where a pitcher was facing hitters for the third time through. That hasn't really manifested yet, in part because there's only been about a dozen "opener" games, and in part because since Romo's first start, they've had nine relief appearances of at least five innings, somewhat negating those effects. Some of this is just too soon to say.
Tampa Bay won't pitch like this all year, because journeymen like Font and Nuno have shown no track record of this kind of success, because "the opener" is not a secret potion, and because this is simply not baseball's best pitching staff.
The Rays are better than you think, though. Snell really is this good. Archer has been in the past. Despite the narrative of the offseason, the Rays really haven't missed Alex Cobb or Jake Odorizzi, and "the opener," while still unproven, remains a valid experiment built on sound reasoning. It's just not the reason Tampa Bay is succeeding -- not yet.