The Milwaukee Brewers traded a mainstay of their rotation in Yovani Gallardo to the Texas Rangers last week, as you by now are well aware. When a team trades a mainstay of its rotation, it’s natural to look to the rest of the rotation in an attempt to find who will pick up the slack. Literally, that person will be Jimmy Nelson, who is likely to fill the now-open spot in the rotation. But Nelson’s a fifth starter who is 26 has thrown just 79 innings in the MLB, so the expectations of him are somewhat tempered.

You look to the rest of the rotation and you see Kyle Lohse and Matt Garza, two guys whose career trajectories appear to be going down rather than up. Mike Fiers is an interesting case, but believe it or not he’s only a year younger than Garza and since he hasn’t been a big part of the rotation the last two years, the bar isn’t set too high for him, either.

This brings us to Wily Peralta. Peralta is young — he’s just 25. Peralta has been a fixture of the rotation the last two seasons — he’s made 32 starts in each year and racked up 382 innings in the process. Peralta legitimately improved last season — he dropped his ERA-, FIP- and xFIP- while throwing more innings per start. And Peralta is exciting, because he throws really, really hard. But that’s the part I want to talk about.



He’s exciting because he throws really hard, but he’s also not-so-exciting because that speed doesn’t actually lead to any strikeouts. Here’s a table of starting pitchers, sorted by velocity next to K%. Peralta sticks out like a sore thumb, alongside Nathan Eovaldi, whom Eno wrote about here. Granted, Peralta saw a boost in his strikeouts last year, but so did most pitchers. Peralta was coming from Mark Buehrle strikeouts levels and he only improved to Aaron Harang levels, so that dims some of the shine of his boost. His 18.4% strikeout percentage and 8.5% swinging strike rate were still well below league average, which is a bit befuddling for a guy who can do this:

That’s a 98mph heater blown past Peralta’s now-teammate Adam Lind. Peralta’s fastball averaged 96.5mph last year, which was a top-10 mark in baseball and a full tick faster than what he averaged the year prior. But still, no whiffs.

A big fastball is one of the most easily recognizable and sought-after things in baseball. It’s simply intuition that velocity would be positively correlated with getting swinging strikes and ensuing strikeouts, but here’s a plot to back up that assertion anyway:

It’s clear that Peralta is unique in this regard. It’s clear that he’s got the stuff to be a strikeout pitcher, but isn’t. And it’s clear that if he is to become a dominant starting pitcher like the Brewers surely hope he will, that getting some strikeouts could go a long way. Though to be fair, that much is true for just about any pitcher.

So why aren’t the strikeouts there? Let’s investigate.

Peralta mainly throws three pitches: a fastball, a sinker and a slider. And perhaps that’s clue number one. Peralta’s fastball and sinker both went more than 96mph on average last season, and they accounted for two out of every three pitches Peralta threw. The third is a slider that goes 86mph, and while a 10mph differential is nice, hitters only have two speeds to worry about. They know they can sit on 96 the majority of the time, and they know they won’t ever see anything slower than 86. Peralta has experimented with a changeup, but he’s never thrown it slower than 84, so even that wouldn’t accomplish the goal of giving hitters a third speed to worry about.

I decided to investigate each of Peralta’s three pitches and their respective swinging strike rates to find the main culprit for his lack of strikeouts. These figures are represented in standard deviations above or below league average:

Fastball: -0.7

-0.7 Sinker: +1.0

+1.0 Slider: +0.7

It’s the fastball. Peralta’s heater got whiffs on just 12% of its swings last year, which is a full percentage point lower than entirely-boring Colby Lewis. That seems odd. Pitch location can have a lot to do with whiff rates, so that seemed like the next logical place to look. I picked three pitchers with similar velocity to Peralta who get significantly higher swinging strike rates on their fastball in hopes that something would pop out. I generated heatmaps, via BaseballSavant, of their fastball location. And I stuck all four into one image, which looks literally exactly like this:

Again, Peralta is unique.

Danny Salazar, another three-pitch guy, works almost exclusively in the upper-third with his heater, leaving the bottom third for his splitter and slider. Jeff Samardzija is a five-pitch guy who also lives almost exclusively up in the zone with his four-seamer. Zack Wheeler throws four pitches, and while he tends to favor the outer edges of the plate with his fastball moreso than the upper-third, he still stays away from the bottom-third.

Peralta, on the other hand, lives mostly low in the zone with his four-seamer and often goes low-and-away to righties — counter-intuitive for someone with the velocity he possesses. Perhaps it’s an organizational thing? Only six teams had their starters pitch to more contact than the Brewers last year, so maybe the team just values weak contact over strikeouts.

If it’s ground balls the Brewers want from Peralta, it’s ground balls he’s getting. All three of his pitches are above-average at generating grounders, and he was just outside the top-1o in grounder rate among starters last year. Grounders are nice, but strikeouts are better –especially with what appears to be an average-at-best infield defense in Milwaukee. And it doesn’t take an extreme skillset to a be a pitch-to-contact guy. It does take an extreme skillset to be a strikeout guy, and by velocity, Peralta has a major part of that skillset.

I explored several different avenues in hopes that something obvious would pop out that could help explain why Peralta doesn’t miss any bats, but came up mostly empty. One more thing I did feel was worth sharing is this usage table from last year, via BrooksBaseball:

It’s a bit unique to see such extreme shifts in usage per situation. Peralta almost never throws his slider when he’s behind in the count, meaning hitters can just sit on 96. On the contrary, he really ramps up his slider usage when he gets ahead in the count and has two strikes, throwing it more than 40% of the time. Maybe game theory is in play here? We already made a point of Peralta only giving hitters two speeds to worry about, perhaps his usage amplifies that problem to some extent.

That’s all I’ve got. Wily Peralta, in some ways, is confounding. He owns what appears to be electric stuff that generates less-than-electric results. There isn’t one obvious thing that jumps out, to me, that explains his complete lack of whiffs given his velocity. It might have something to do with the fact that he doesn’t change speeds too often. It might have something to do with the fact that when he does change speeds, all he has is a slider that’s more average than it is great. It might have something to do with him throwing his fastball down in the zone so often, which might be an organizational thing. It might have something to do with predictable usage patterns. It might be (probably is) something else that I missed entirely.

Peralta made improvements across the board last year and turned into a pretty useful pitcher, so maybe this isn’t even something he wants to change. But on the surface, it feels like you should be able to see some strikeouts in Wily Peralta. We just haven’t seen them yet, and the surface is thick.