Who is Tyler Thornburg?

The Red Sox took the baseball world by storm on Tuesday, making two major trades and then signing Mitch Moreland for some reason. Obviously, the Chris Sale trade has dominated the headlines. He’s undeniably the best player who has changed uniforms this winter, and the Red Sox sent arguably the best prospect in baseball to Chicago along with one of the more exciting young arms in any organization. It also gave the team a fearful top-three, and played into the narrative of Dave Dombrowski not giving a damn about farm system rankings. Many words have been written about the implications, and many more will be written in the near and long-term future. I will probably even write some of these words, but not today. Today, I want to look at the first deal the Red Sox made on Tuesday.

That day was started with the trade that sent Travis Shaw, Mauricio Dubon (sad face) and Josh Pennington to Milwaukee for Tyler Thornburg. We’d been expecting a move that brought an eighth-inning arm to the Red Sox, and we got it with this deal. While he’s certainly not as impactful or as exciting as Sale, Thornburg can be expected to slot right behind Craig Kimbrel on the bullpen depth chart. Since he’s been overshadowed by the deal with Chicago, one that came just a few hours after this one, I thought it’d be worthwhile to take a look at what exactly Boston acquired with the former Brewers pitcher.

To go back to the beginning (mostly), Thornburg was drafted out of college by Milwaukee in the third round of 2010 draft. Prior to the 2013 season, he was ranked the number 100 prospect by Baseball Prospectus, the only time he made a top-100 list, per Baseball-Reference. After spending his minor-league career as a starter, 2016 was his first full season of focusing solely on relieving.* It went swimmingly, as he pitched to a 2.15 ERA (50 ERA-), a 2.83 FIP (66 FIP-) and a 2.89 DRA (80 DRA-). Put more simply: He was super good. Of course, this was also his first successful full season in the bigs, so let’s take a little bit of a deeper look at the 28-year-old and see what kind of pitcher he really is.

*He hadn’t made a major-league start since 2013, but was still starting in his Triple-A stints.

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For starters, Thornburg is a righty. This is important for relievers, of course, as matchups come into play more often for them, and being vulnerable against opposite-handed hitting can be lethal to a late-inning reliever. It’s even more important for a Red Sox team that is missing a dominant left-handed option. Luckily, Thornburg hasn’t shown any worrisome splits. In fact, last season he was the owner of massive reverse splits, both in terms of OPS allowed and FIP. The difference over his career isn’t quite as large — and the sample isn’t large enough to buy into completely — but the reverse splits are still there. The biggest eye-opener are his strikeout numbers based on handedness. Last season, he struck out a whopping 40 percent of opposing lefties compared to 30 percent of opposing righties. Even if the reverse splits aren’t for real, there’s at least no reason to worry about him getting killed by lefties, which is a nice start.

Beyond the splits, it’s also worth noting that Thornburg is an extreme fly ball pitcher. Per Fangraphs, only 13 of the 273 pitchers that reached the 60-inning mark allowed ground balls at a lower rate. According to Baseball Prospectus, 25 pitchers had a lower ground ball rate. That’s a scary thing in the AL East, but we’ve seen pitchers overcome it before, and the Red Sox are in a good position to deal with it now. Barring a shocking development in the next couple months, Boston will have Jackie Bradley, Mookie Betts and Andrew Benintendi — three legitimate center fielders — manning their three outfield spots. They obviously can’t do anything about balls that go over the fence, but this team is better off than most in counteracting fly ball tendencies.

So, the splits and the fly ball tendencies are both inherent parts of Thornburg’s game, but he took a huge step forward last year. Let’s take a look at why. Starting with the plate discipline numbers, it’s obvious. He missed more bats than ever before. His 28 percent swinging strike rate (per BP) was a career-high, well above-average and led to his 12 strikeouts per nine innings. Along those same lines, he saw a massive decrease on contact on pitches in the zone with a rate that put him around some of the best relievers in baseball last year. Getting swings and misses on balls out of the zone is more aesthetically pleasing (at least for me), but those who get the most swings and misses on balls in the zone are generally among the most effective in the game.

The reason for this is a couple of changes in his repertoire after switching to relief full-time. Thornburg started by mostly phasing his changeup out of his toolbox, still throwing it some but relying much more heavily on a fastball/curveball combination. The shorter stints and smaller repertoire helped that stuff play up, as is evidenced by his strikeout rate, plate discipline numbers, and velocity. His average fastball climbed from just under 93 mph in 2015 to just over 95 mph in 2016, a massive jump for one year.

His curveball turned into his money pitch, though. He threw it roughly a quarter of the time last year, and it turned into his best offering. Thornburg induced whiffs on 43 percent of swings against the pitch and induced ground balls on half the balls in play it allowed. It’s worth noting, however, that he also had some home run issues with the pitch. Still, it was the go-to offering that made his improved fastball work, and the command was a big reason the curveball was so effective. He did a remarkable job keeping the pitch down, with just a few instances of the ball staying up in the zone ready to be crushed. Here, you can see it fooling someone as great as Kris Bryant.

Thornburg was not the most exciting acquisition by the Red Sox on Tuesday, and he won’t be the most important either. But he does figure to play a major role on this team, despite having just one good year of experience. Despite that, he should be a strong addition. He doesn’t have splits you need to worry about late in games, and his fly ball tendencies can be counteracted with an outstanding outfield defense. Plus, his one year of good performances is backed up by legitimate changes that come with a first full season as a reliever. Thornburg is no Sale, or even a Jansen or Chapman, but he’s a worthy eight inning man to Craig Kimbrel’s ninth inning.