The ERA certainly jumps out, but most amazing is the implied 29.0 strikeout-to-walk ratio. That's dominance at the command-and-control level you rarely see, even over such a small sample. Twenty of those 29 strikeouts have been of the swinging variety. Just 10 times this season has a batter reached a three-ball count against Berrios. We could go on, probably. For instance, he hasn't issued a walk in more than three weeks.
Anyhow, it's perhaps too much to say Berrios is working on a breakout. After all, last season, when the Twins made the playoffs, Berrios pitched to a solid 112 ERA+ with 139 strikeouts in 145 2/3 innings. Throw in the fact that he was once a consensus top-10 overall prospect, and it's clear that Berrios isn't coming from nowhere in 2018. When you're dominating like this, though, it stands out no matter who you are.
So what's going on? Well, in broad terms we're talking about a highly promising young pitcher who's gaining experience at the highest level, moving closer to his prime, and making the gains associated with all of that. More generally, Berrios seems to be putting the finishing touches on the some tweaks he made in advance of last year's step forward. First, his velocity's up just a bit in 2018. Second, he's continuing with the more balanced pitch mix that he shifted to last season. Note, for instance, the declining use of his four-seamer relative to his rookie season of 2016, when he was mauled to the tune of an 8.02 ERA in 14 starts ...
In 2018, the fastball remains his go-to, but he's throwing it just 38 percent of the time now compared to more than 50 percent of the time in 2016. As well, he's getting movement on two planes from his breaking ball, and batters are whiffing at it more than 20 percent of the time. In matters related, batters are hitting just .095 against that curve.
Berrios also raised his arm slot last season, and this year he's raised it a bit more. Another notable tweak is his positioning on the rubber. Take a look at how he's shifted from the first base side of the runner to the third base side ...
As you can see, Berrios as a rookie -- en route to allowing 56 runs in 58 1/3 innings -- was on the extreme first base side of the rubber. In 2017, he shifted to the third base side. As the magnifications of his foot show, this year he's even further to the third base side. Last season, his toes were pretty much flush with the rubber, and this year there's some overhang (this appears to be the case regardless of the hitter's handedness). Presumably, this gives him better attack angles -- maybe he can make same-side hitters a bit more comfortable and more easily back-door the opposite side. Whatever the case, that's almost certainly got something to do with his better results.
Add it all up, and, as Minnesota manager Paul Molitor recently said of Berrios, "He's throwing better than I've ever seen him."
No, he's not going to keep up this level of dominance (that .209 BABIP probably isn't sustainable over the long-term), but Berrios' complete mastery at the strikeout and walk level certainly bodes well for the future. Throw in the various factors that help explain his leap forward, and Berrios is looking very much like a present and future ace in Minnesota.