Freddy Peralta didn't exactly come out of nowhere. He made the Midwest League All-Star team in 2016 and the Carolina League All-Star team in '17. Peralta struck out 169 batters across 119 1/3 Minor League innings last year, a 33.4-percent rate that, if it were done in the Majors, would have been a top-five number among starting pitchers.
But Peralta is only 5-foot-11, and his fastball averages only 91.2 mph -- and he throws it more than 80 percent of the time. That's not exactly a profile that gets you a lot of favorable grades on scouting reports, and it didn't. Then Peralta struck out 13 at Coors Field in his debut, then 10 more in his Miller Park debut last week. In fact, he has become the first pitcher on record (since 1908) to have at least five strikeouts while allowing three or fewer hits in each of his first four games.
So as Peralta enters game No. 5, facing Matt Harvey and the Reds on Sunday, it's time to investigate. How does a short righty with below-average velocity who throws his fastball four of every five pitches manage to collect so many whiffs?

The answer seems to be in something that's long been extremely difficult to quantify: deception. Just look at how his teammates and opponents speak about how the ball looks coming out of his hand.
"It is hard to explain," said Royals manager Ned Yost to MLB.com's Adam McCalvy on Wednesday. "He's got a high spin rate, and the ball just kind of jumps on you even though it's 92 mph."
"It was unbelievable," said Brewers first baseman Jesus Aguilar after Peralta's debut against the Rockies. "I've never seen their second baseman [DJ LeMahieu] look like that, or [Charlie] Blackmon. They didn't see the ball. Good for him. These are really good hitters, and he dominated, easy, with the fastball."
"I would hate to face that guy," Milwaukee outfielder Keon Broxton noted to the Wisconsin State Journal. "He's throwing invisible fastballs up there. One pitch, and the guys can't hit it. That's frustrating as a hitter."
So let's talk about Peralta's "invisible" fastball, and the first thing to know is that it's probably not just one fastball. It's a "power cutter/sinker thing that does something different every pitch," Christian Yelich said recently.
Peralta explained. "It's a different grip. I throw it, and the ball just goes."

That may be, but for our purposes, it's classified as a four-seam fastball, and even if it were two different pitches, we'd probably combine them to look at his overall fastball rate anyway. Dating back to 2008, when reliable pitch-tracking came online, there have been more than 2,500 seasons from starters who have thrown at least 20 innings. Peralta ranks in the extreme.
Highest fastball rate among starters from 2008-18 (minimum 20 innings)
82.6 percent: Daniel Cabrera, 2008
81.7 percent: Tony Cingrani, 2003
80.3 percent: Peralta, 2018
78.4 percent: Micah Owings, 2011
77.0 percent: Chris Young, 2010
That's not exactly a list of highly productive pitchers, yet look at just how good Peralta's fastball has been so far. We've seen 119 starters who have had at least 50 plate appearances end on a four-seam fastball, and Peralta's ranks are outstanding.
First in batting average, .086, ahead of Carlos Martinez
First in slugging percentage, .155, ahead of Martinez
First in wOBA, .181, ahead of Walker Buehler
Fourth in swing-and-miss rate, 32.5 percent, ahead of Jacob deGrom and Chris Sale
Now keep those in mind, and remember where Peralta ranks in velocity, this time of 190 starters who have thrown at least 50 four-seamers. 
130th in velocity, 91.2 mph, between Jake Faria and Trevor Williams.
So we know the fastball isn't thrown hard, but it's thrown a lot, and it has (so far) led to elite success. How is that possible?

The quotes above give us a clue, particularly Yost's reference to "high spin rate." So does this snippet of a scouting report from our friends at MLB Pipeline, who had Peralta ranked as Milwaukee's No. 9 prospect:
"Peralta makes up for being an undersized righty by generating enormous extension to plate," wrote the report, "causing his low-90s fastball that touches 94 mph to play up consistently."
They're both right. Looking at those same 190 starters who have thrown 50 fastballs, Peralta ranks 14th, or in the 93rd percentile in average spin rate. Like high velocity, high spin rate doesn't by itself make you good, but it's a nice tool to have, as it can help in giving the "rising fastball" effect, which correlates well to swinging strikes and fly balls. Some of the names ahead of him include Justin Verlander and Max Scherzer, though the presence of Jeff Samardzija and Mike Minor reminds you that there's more to his success than simply a high spin rate.
Still, the high spin makes it notable, as does the extension. That's measured in feet, in terms of the point off the mound the pitcher releases the ball. Another way of thinking of that is that while the pitching rubber may be 60 feet, 6 inches away from the plate for everyone, each pitcher has a different release point.
Some pitchers don't even get to five feet of extension, and the Major League average is about six feet. Peralta's extension, meanwhile, is more than seven feet, the highest of our 190 starters. He might throw only 92, but it has to travel less distance than other pitchers, and it does it with higher spin. Putting both fastball spin and release extension on the same scale for starters, you can see that Peralta is an outlier.

There's also the matter of his height. If we turn now to all pitchers, looking only at the 347 who have thrown at least 100 four-seamers, we find that the average height is 6-foot-3 inches. Peralta, listed at 5-foot-11, is on the shorter end of that scale. In fact, only 11 pitchers are shorter than him, and several of those (like Kazuhisa Makita and Kelvin Herrera) don't exactly fit his profile.
Interestingly, however, one of those 11 does seem to make some sense as a comparison here in terms of a short, right-handed, fastball-heavy pitcher who fills the zone with relatively low-velocity heaters, and who can also manipulate that pitch to do different things: Bartolo Colon. (The current version, anyway. When Colon was Peralta's age, he was a legitimate flamethrower.)

Somewhere in there, in that combination of having a higher spin rather than the average fastball delivered from closer to the plate than any other starter, from a pitcher who is shorter than most other starters, is our answer to how Peralta can survive -- prosper, really -- despite a lack of velocity or a large repertoire.
It might get us part of the way toward explaining "deception," an elusive term that nonetheless can play a big role in why certain pitchers do or don't succeed. It doesn't get us all the way there, of course, because there's also something to be said for how the pitcher hides the ball (or doesn't) during his motion, which we can't quantify yet.
It doesn't fully explain Peralta's success, either. But he didn't just come from nowhere to do this, either. Peralta has been doing this for a few years in the Minors. So far, it has translated to the bigs, and that's a pretty huge deal for a first-place Milwaukee club that needs all the rotation help it can get.