Original story published by Jack Stern on Brewer Fanatic.
MILWAUKEE — It’s become a familiar story in Milwaukee: an unheralded reliever joins the Brewers, refines his arsenal, and becomes a contributor in the big-league bullpen. When one such success story landed on the injured list, the club replaced him with someone who could become the next.
When breakout reliever Jared Koenig hit the injured list over the weekend with forearm inflammation, the Brewers called on another left-handed minor-league veteran to replace him, selecting the contract of Rob Zastryzny.
Signed to a minor-league contract in December, Zastryzny has had a strong season with the Triple-A Nashville Sounds. In 28 ⅓ innings, he posted a 3.18 ERA and 3.07 FIP, with an excellent 34.2% strikeout rate.
“He’s the next man up,” Pat Murphy said. “I think he threw the ball well. He’s a veteran. He’s been around. He’s been around this league.”
The 32-year-old has appeared in parts of five MLB seasons with four teams and owns a career 4.70 ERA, with a 1.63 strikeout-to-walk ratio in 59 ⅓ innings. That unremarkable body of work is not representative of the current version of Zastryzny, who could be more than a short-term placeholder in the big-league bullpen.
Zastryzny’s strikeout rate is the highest of his professional career, and the product of a few changes to his arsenal. Those adjustments began before he joined the Brewers organization, but Milwaukee’s pitching development brass has helped him perfect them this year.
A second-round pick of the Chicago Cubs in 2013 as a starting pitcher, Zastryzny progressed through the system, attempting to maintain a traditional starter’s arsenal. During his first three MLB seasons with the Cubs, he featured a curveball and a short slider as his breaking pitches. The curveball featured below-average movement, which he later learned was because he struggled to topspin the ball from his arm slot.
“It wasn’t truly a curveball,” he reflected. “It had negative one or two [inches of induced vertical break] for the most part. It was just kind of a slow gyro slider. I’ve never been able to spin the ball with topspin, and I thought for years that’s what I was doing.”
Once exposed to his pitch shape metrics, Zastryzny discovered he was better at generating sidespin than topspin. His approach to his secondary pitches shifted to maximizing the former.
“Whenever we figured that out, it was like, ‘Hey, you’re not gonna get on top of the ball, maybe you can get on the side of it and make the ball move [to the] right.’”
PREVIOUSLY FROM BREWER FANATIC: How can the Brewers’ run prevention infrastructure benefit Dallas Keuchel?
The pitching development crew at Push Performance in Arizona, where Zastryzny trains during the offseason, and Texas-based pitching coach Scott Lacey encouraged him to replace his previous breakers with a sweeper. Such a breaking ball relies on sidespin to produce greater lateral movement, with less drop.
In 2018, the last year Zastryzny threw his curveball in the big leagues, it averaged 4.9 inches of horizontal break. The sweeper has averaged 12.4 inches this year.
While encouraged by the results of his new breaking ball, Zastryzny realized it had its limits. The sweeper is primarily a chase pitch for swings and misses down and away, and can be less effective against opposite-handed batters.
“It ended up playing pretty well against lefties, especially,” he said, “but it’s a hard pitch to land in-zone a lot.”
Zastryzny needed another pitch he could use more aggressively in the strike zone and throw to right-handed batters, so he added a cutter to his arsenal as a middle ground between his four-seamer and sweeper. While splitting time between the Pittsburgh Pirates and their Triple-A team in 2023, he used it 22.6% of the time.
“The more I threw it, the more I realized that it plays both left and right, and it can get weak contact and strikeouts,” Zastryzny said. “So I figured if I have a pitch like that I can command better than the sweeper, I should up the usage of it.”
The Brewers took notice of the cutter and expressed interest in Zastryzny over the offseason. It was a natural fit for both parties, as each wanted to make the cutter an even more prominent part of his arsenal.
“The first thing they told me was, ‘Hey, we see this pitch that you’re using about 12, 15 percent of the time. Do you think you can use it about 25, 30?’ And I said, ‘That’s exactly what I want to do.’ So it was a good match.”
In addition to upping its usage to 33.8% this year, Zastryzny has utilized the cutter more diversely across the strike zone. He started back-dooring it to right-handed batters and using it at both the top and bottom of the zone.
“As soon as I got here this year, that’s all we did,” he said. “It was like, ‘Where do you want to throw it? Who do you want to throw it to? What does it set up?’ And from there, it’s been really good in Triple-A.”
PREVIOUSLY FROM BREWER FANATIC: At bat, the Milwaukee Brewers are master managers of the count
The cutter serves several functions, but its greatest impact may be how much it’s boosted the effectiveness of the Zastryzny’s four-seamer, which is now a weapon at the top of the strike zone. Opponents have slugged .170 against it, with no extra-base hits and a 27.8% whiff rate. That whiff rate was 21.6% last year.
The fastball and cutter play off each other. Zastryzny has emphasized tunneling the two, which look alike out of his hand due to their similar spin axes but have distinct velocities and paths through the zone.
“It looks enough like the fastball to where it can get under a bat, but it also gets guys off the four-seam fastball at the top,” he explained.
Paring down Zastryzny’s arsenal to a four-seamer, sweeper, and slider made formulating an approach against each of those pitches easier. The cutter has disrupted that.
“Last year when I was with the Pirates, you see something up, you’ll just assume hard. If you see something down, you can assume soft. And it just becomes a more comfortable at-bat. Now with the cutter that I throw up and down, it means I’m throwing a high-80s pitch at the top and the bottom, so you can’t just sit low soft, high hard anymore.”
In addition to making the fastball less hittable, the cutter also helps him steal more strikes with it. The called strike rate of his four-seamer has jumped from 16.9% to 21%.
“A lot of the times, if I go down-and-in cutter to a righty, I can go down fastball off of that,” he said. “And if they even assume cutter at all, they’ll take, and I’ll get a free strike there.”
With the four-seamer, cutter, sweeper, and changeup, Zastryzny has developed a pitch mix that maximizes how the baseball behaves as he slings it from his low three-quarters release slot.
“I think that’s what analytics does,” he said. “A lot of people are like, ‘Hey, you can go to this pitch lab with either the Brewers or in the offseason, and you can create whatever pitch you want.’ But in reality, it’s just figuring out what you do well and going off that.”
The refined version of Zastryzny made his Brewers debut as the opener for Bryse Wilson on Monday in Colorado, tossing a perfect first inning. With Koenig sidelined through the All-Star break, he’ll likely get at least a few weeks to prove that his stuff can play against MLB hitters. It would not be surprising if Zastryzny added his name to the growing list of minor acquisitions to unlock their best stuff with the Brewers and contribute out of the bullpen.
PREVIOUSLY FROM BREWER FANATIC: What do the Juan Soto and Eduardo Rodríguez deals mean for the Brewers?