Justin Slaten is well on his way to becoming a Rule 5 success story. Selected by the Mets out of the Rangers organization this past December and subsequently swapped to the Red Sox on the same day, the 26-year-old right-hander has come out of the Boston bullpen eight times and relinquished a single run in 14 1/3 innings. Moreover, he’s been stingy with baserunners, allowing just six hits and a pair of free passes. Four weeks into the season, he’s been the team’s top reliever.
His lone low moment to date came in his major league debut. Pitching in Seattle in the third game of the season, Slaten surrendered a 10th-inning walk-off single to Julio Rodríguez on his fifth big league pitch. Since that time, he’s been borderline flawless — opposing hitters have gone a paltry 5-for-45 against his power arsenal, with a Mike Trout triple accounting for the only extra-base knock. He’s punched out 14 batters.
Slaten’s mix — 38.5% cutters, 35.2% sweepers, 24.0% four-seamers, 2.2% curveballs — has been more varied than he expected it to be when he broke camp. Other than that, he’s mostly the same hurler who attracted Rule 5 interest by overpowering hitters while pitching with the Rangers’ Double-A and Triple-A affiliates last year.
“My only approach coming in was to throw everything in the zone, trying to get the best results,” Slaten told me before a recent game. “The only thing that has changed a little bit is the pitches that have been called. I’m probably throwing a higher percentage of breaking balls than I have in my entire life. But nothing has changed about the way I throw them, or try to execute.”
The extent to which he fills up the strike zone has been a meaningful change. His ability to miss bats has never been an issue; command was — until last year. As our lead prospect analyst Eric Longenhagen wrote back in July, Slaten “has late-inning stuff and seems to have taken a step forward from a control standpoint.”
Going into attack mode helped him turn a corner. Improved mechanics — “nothing super major” — has been a factor, too, but the realization that he could pound the strike zone without incurring much damage is what mattered most.
“I had a couple of rough years in the minors, trying to really focus in on some of the stuff that the Rangers were telling me,” said Slaten, who was drafted in the third round out of the University of New Mexico in 2019. “It wasn’t until last year in [Double-A] Frisco when I started having a good season. That was kind of when I fully started believing in myself, believing, ‘OK, my stuff is really good’ and that I have to trust it. Knowing that your stuff is going to play in the zone — you can basically go out there and force swings — makes pitching a lot easier.”
There have been two other impactful changes, as well. One was transitioning to the bullpen, which he began doing in 2022. The other is the development of his cutter, a pitch that Slaten “started implementing last season and really helped in taking that next step.”
As for his other pitches, he began throwing a curveball shortly after entering pro ball — “it was kind of a little toy that they wanted me to play with” — while the sweeping slider has been part of his repertoire for years. He told me prior to this season that he considers his slider to be his best secondary pitch, if not his bread and butter.
His heater, which is averaging 96 mph and occasionally flirts with triple digits, has been his best pitch this season from a statistical standpoint. Slaten has thrown 43 four-seamers and has yet to allow a hit against the pitch. Elevating the offering is part of his M.O. on the mound.
“I would say that it’s a power fastball — your prototypical power fastball — and I’m going to throw it in the mid- to upper-90s,” Slaten said. “I’m a high vertical-ride guy. On average, I’m probably right around 17-18 [inches], but on my best days I’ll push it up to 20-21, sometimes 22. It’s a pitch that I have a ton of confidence in.”
Confidence is a centerpiece of Slaten’s success story. Trusting that he can essentially aim middle and allow his power arsenal to play in the zone jumpstarted his career and helped get him to the big leagues. His confidence level has only grown since his arrival in The Show.
“The first weekend, anticipating that first time taking the field as a big leaguer, was maybe a little [nerves],” said Slaten. “But as far as being out there on the mound, that’s the one thing everybody has told me is the same — it’s the same game, no matter where you’re at. Once you start getting big league hitters out, you kind of realize, ‘OK, maybe I do belong here.’ Any feeling of uncertainty I might have had when I first got called up has gone away.”
