I’ve gone around and around on this point. It’s possible that J.A. Happ is the best starter on the market. I used to think Tyson Ross would be the best starter on the market. And the Mets, of course, could blow everyone away if they start taking real offers for Jacob deGrom. There is no clear favorite; the trade-deadline picture is always cloudy. But I can tell you I’m coming around on Nathan Eovaldi. Eovaldi is eight starts into the season, now that he’s on the other side of Tommy John surgery, and he’s already recorded three starts of at least six innings with no more than one hit. On Sunday, against the Mets, he made an attempt at a perfect game. All of Eovaldi’s old arm strength remains intact. And now he’s improving on what he does with it.

Back when Eovaldi was younger, back when we understood a little less about pitching, he was somewhat confounding to analysts. It didn’t make immediate sense why someone who threw so hard would allow so much contact. Where we stand today, Eovaldi has what would easily be a career-high strikeout rate. He also has what would easily be a career-low walk rate. I can rattle these things off if you’d like. Among starters this season, Eovaldi ranks first in strike rate. He ranks second in chase rate. He ranks first in the rate of pitches thrown while ahead in the count. He ranks first in the rate of pitches thrown in the zone. Eovaldi is blossoming, and you could argue he has the Yankees and Rays to thank.

It was the Rays who signed Eovaldi as a free agent. They signed him knowing he wouldn’t be available to pitch in 2017. He’s got a low 2018 base salary, similar to Tyson Ross, and that’s part of what makes him appealing in a trade. The rest of what’s appealing is the talent. At the time that Eovaldi got injured, he was pitching for the Yankees. He was also with the Yankees the season before. Eovaldi was able to throw hard from the beginning, but the Yankees got him to change how he thinks about his fastball.

If you know anything about the Yankees’ pitching staff, you probably know that it shies away from the fastball, even though most of the fastballs are good. No team throws a lower rate of fastballs than the Yankees do. Here is a plot of Eovaldi’s career fastball rates. This includes both four-seamers and two-seamers.

Eovaldi’s two-seamer disappeared early. And then, upon joining the Yankees in 2015, he moved toward throwing fewer four-seamers. That adjustment has stuck, even after changing teams. Right now, Eovaldi ranks third among starters in fastball velocity. He ranks 168th among starters in fastball rate. There are 25 starters in baseball with an average fastball velocity of at least 95 miles per hour. Only Eovaldi and Shohei Ohtani have thrown their fastballs less than half of the time. You can see part of what’s going on — Eovaldi has been convinced not to just lean on his heat, simply because his heat is really hot.

Then there’s something else that happened with the Yankees. It happened fairly late in the game. I remember exchanging emails with someone about it, thinking about a potential post, but then Eovaldi got hurt. In any case, shortly before Eovaldi went on the DL, he started throwing a low-90s cutter. That adjustment has also stayed with him.

The cutter now moves a little different from how it did, but not by much. This has turned into Eovaldi’s favorite secondary. In 2016, when ahead in the count, Eovaldi threw 41% fastballs. This year, that’s basically unchanged. In 2016, when even in the count, Eovaldi threw 44% fastballs. This year, that’s basically unchanged. In 2016, when behind in the count, Eovaldi threw 57% fastballs. This year, that’s down to 39%, with the cutter taking over. The cutter has come on strong, giving Eovaldi a pair of pitches he trusts that get on the hitter in a hurry.

With the Yankees, Eovaldi reduced his fastball usage. With the Yankees, he picked up a cutter. Enter the Rays. With the Rays, one thing Eovaldi has done is aim his fastball considerably higher. You’ve heard about the Rays and the high fastball before. Eovaldi doesn’t have a classic high-spin heater, but you don’t necessarily need one in order to succeed in the upper half. Here’s a plot of Eovaldi’s entire career, with rolling-average fastball heights, expressed in feet:

To show it a different way, here are Eovaldi’s fastball-height percentile ranks:

Eovaldi didn’t work up in the zone very much. He didn’t throw his fastball as if it were a sinker, either. On average, Eovaldi used to hang around the vertical middle. Now, Eovaldi is throwing his fastball higher than almost any other starter. It’s similar to what the Rays did with, say, Drew Smyly. While Eovaldi’s heater doesn’t get that extreme rise that other pitchers generate, it’s still a matter of establishing different areas of the zone. Eovaldi now attacks into and beyond the upper third.

And then there’s just been another, more subtle thing. Here are heat maps for Eovaldi in 2016. On the left, his fastballs; on the right, his cutters.

Compare that to Eovaldi in 2018:

The fastballs are higher. We knew that. But look at the cutters. Before, when Eovaldi was just learning the pitch, he threw most of his cutters glove-side. Now he’s bringing his cutters more over the plate. What’s important here is how the cutter appears, relative to the fastball. This gets right into the concept of pitch-tunneling. There’s not all that much movement difference between the fastball and the cutter. Therefore, the locations shouldn’t be too far apart, or else it’ll be easier to tell which is which. By bringing the fastball and cutter closer together, Eovaldi is allowing them to play off one another. And he throws so hard to begin with, the hitter has very little time to react.

As an example, here’s a 3-and-1 cutter from a couple weeks back:

There’s contact, sure, but the contact is worthless. Then comes the full-count heater:

One example is only one example, but the cutter was thrown to set up the fastball. The pitches followed similar planes, but the cutter dove slightly, while the fastball stayed up. Eovaldi salvaged a 3-and-1 count, getting a foul and a strikeout. That’s exactly how that’s supposed to work, if you have to pitch in a three-ball count in the first place.

Reduced fastball usage. Increased cutter usage. Increased fastball height. Improved fastball-cutter tunneling. Eovaldi still throws his slider, splitter, and occasional curve, but the big changes have been with the primary two pitches, and in so many ways he comes off as something of an analytical success story. He’s been a breath of fresh air for the Rays, helping them work through a shortage of available pitchers. And while the Rays would prefer to be in a better deadline position in the standings, there’s little to be done about that now, and Eovaldi has made himself awfully appealing to other teams in the hunt. Given that he’s still just 28 years old, it stands to reason he could have a lot of career left to go.