Freddy Peralta is showing he’s a starter

After spending the last two years in the bullpen, Freddy Peralta had to prove he belonged in the rotation. Peralta put up a strong spring and won the fifth spot over Josh Lindblom and a month into the season, he’s showing no signs of giving it up.

Peralta’s lone relief appearance came on Opening Day, but he’s been in the rotation ever since. All he’s done as a starter is post a 3.11 FIP in five starts, which would be great for someone at the top of the rotation, but it’s even better coming from someone who had to fight for a spot in spring training.

In 28 innings, the righty has struck out 45 batters including 7 in 6 innings against the Dodgers in his most recent start. Among qualified starters, Peralta ranks fourth in strikeout percentage with a 40.2 mark, sandwiched between Gerrit Cole and Shane Bieber. 2020 was a high-water mark for Peralta’s strikeout rate at 37.6 as he hovered around 30 percent in his first two years in the majors.

He owes the jump to a change in pitch mix. Peralta has essentially been a two-pitch pitcher throughout his career, primarily relying on his fastball and curveball while mixing in the occasional changeup. At times, he has looked like a one-pitch pitcher, throwing his fastball more than 70 percent of the time.

Last season, he began throwing a slider but he used it only sparingly. This year, he’s decreased his usage of both the fastball and the curve in favor of the slider. With a more even mix and an effective third pitch, Peralta has become far less predictable. It used to be that if Peralta fell behind in the count, hitters could sit on the fastball. Here’s his pitch mix by count in 2019.

Baseball Savant

In a 2-0, 2-1, 3-0, 3-1, or 3-2 count, Peralta hardly ever went away from his heater. Here’s the same chart in 2021.

Baseball Savant

If he’s behind 3-0, he’ll stick to the fastball, but he’ll throw a slider a quarter of a time in any other count. That’s because Peralta has been far better about throwing his slider for a strike when he needs to. Overall, his slider’s Zone% is roughly the same as his curve’s (roughly 40 percent). When Peralta’s ahead, he’ll throw it outside to try to make the hitter expand the zone and reach for the slider. It’s somewhat effective—hitters have only chased 26.2 percent of his sliders but have missed 80.2 percent of those. When Peralta is behind in the count, however, he’s coming after hitters, throwing the the slide piece in the zone 54.7 percent of the time. That’s as reliable as his fastball.

Baseball Savant

The downside is that it’s a little easier to hit, but it’s still better at generating in-zone swings and misses than the curve. It’s better at generating swings and misses period. So far, Peralta boasts a 50 percent whiff rate on his slider which is up from 37.5 when he debuted the pitch a year ago. That’s thanks to a change in the shape of the pitch.

Last year, Peralta’s slider had more drop than break. Over the offseason, Peralta added eight inches of horizontal movement and it’s easy to spot the difference between the two versions of the pitches. Here’s a slider that Peralta threw down and away in 2020.

And here’s a slider that Peralta threw in the same spot in his last start.

Apologies for the differing camera angles, but the sweeping movement on the latter pitch compared to the looping dive of the former isn’t a trick of perspective. The pitch is turning into a major weapon especially against right handers. At this point of the season, Peralta has thrown exactly as many sliders as he has fastballs against righties and they’ve been helpless against the pitch. Righties have an xwOBA of .152 against his slider and have mostly flailed at it, whiffing on 55.1 percent of their offerings.

Lefties haven’t fared much better against the pitch, but Peralta has used it more sparingly. Peralta has actually gone back to using his changeup against lefties after abandoning it last year, giving him four pitches when he’s at a platoon disadvantage.

If there’s a blemish on Peralta’s season, it’s that he’s still walking 12.5 percent of batters. A five point improvement in his zone percentage from 2020 still puts him in the bottom 15 of qualified starters. Command issues have kept him out of the rotation previously, and they could be what takes him out again. The slider is helping him miss more bats, which in turn is helping him navigate those extra walks, but he’ll need to command his pitches better if he wants to move from the back of the rotation to the front.

Kenny Kelly is the managing editor of Beyond the Box Score.