Since the beginning of August, there have been 185 pitchers to qualify as a reliever. Only one of them has yet to allow an earned run in that time. Some of the first names that might come to mind are Liam Hendriks, Nick Anderson, and Kirby Yates. Nope, it’s none of those three, and for most casual baseball fans, this name would be fairly unrecognizable.
The reliever is Tyler Duffey of the Minnesota Twins. Since the beginning of August, the righty has appeared in 24 games, pitching a total of 21 1⁄3 innings, all scoreless (the last earned run he allowed was on July 23rd). His peripherals have been equally impressive, as he’s struck out 37 batters, compared to only five walks. All good for a 0.60 FIP since August, which also ranks first.
[Editor’s note— this article was written and finalized a few days ago, but for scheduling reasons we weren’t able to publish it until now. Naturally, Duffey surrendered a pair of runs on September 28— his final appearance of the year. As such, the stats presented here are no longer exactly accurate. Duffey is still a really good pitcher though, and the author’s analysis certainly remains valid. Enjoy the rest of the article!]
For those who don’t know, Duffey is your standard failed starter, turned two-pitch reliever, working with a four-seamer/curveball combo. After a serviceable season in 2017, his first as a reliever (71 IP, 4.94 ERA, 3.72 FIP), his performance hit a wall last year, allowing 20 earned runs in 25 innings total, striking out only 19 batters.
After going back down to Triple-A to start the 2019 season and subsequently dominating, the Twins called Duffey back up. He returned to his serviceable self in the first half (3.49 ERA in 28 1⁄3 innings) and after a quick blip in July (6.75 ERA in 9 1⁄2 innings), he’s turned himself into one of the best relievers of the second half of the season (0.95 ERA, 28 1⁄3 innings).
A lot of Duffey’s improvements can be attributed to the fantastic work that new Twins pitching coach Wes Johnson has done. All that Duffey needed was a Spring Training assessment with him.
“A big change came this spring, with Wes Johnson coming in [as the new pitching coach]. He had a plan laid out for us. We all have our strengths and weaknesses and we’ve made it a point to capitalize on those strengths. I’ve gone pretty much strictly to four-seams, which has created a lot of useful movement that plays up in the zone. Being able to throw fastballs in that spot has made my curveball play up.
Duffey’s signature pitch as a reliever has always been his slurvy breaking ball (classified as a slider). Adjustments with the fastball allowed this pitch to play up.
“Over time I’ve messed with the velo on it, and now it’s 85-86 [mph] on a good night. That’s almost like a slider, but I’m not thinking slider — I’m thinking of staying behind the ball and spinning it. And while I’m able to vary the velo from the mid-70s to the mid-80s, the vertical break is actually very similar. The speed change doesn’t change the break. The Twins have basically said, ‘If you throw that hard one, you can throw it as much as you want, whenever you want.’
The first thing that Duffey mentioned in the quote above was his increased reliance on four-seamers. Prior to this season, he had mixed a sinker into his repertoire, but he ended up ditching it this year. Among 315 pitchers with at least 20 innings thrown in 2018 and 2019, only seven had a larger decrease in sinker-rate than him.
Biggest decreases in sinker usage
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What was also brought up was the change Duffey had in his fastball location, with the goal back in Spring Training being to throw more up in the zone. Last year, he was just below the middle of the pack in average vertical fastball location (-0.02 feet ranked 369th out of 629 qualified). In other words, he was throwing a lot of pitches towards the middle of the plate, as evidenced by the heatmap.
This season, his average vertical fastball location sits at 0.24 feet, ranking 156th out of 643 qualified. He’s been littering the top of the strike-zone with his mid-90s fastball.
The adjustment has played out perfectly. The swinging-strike rate on his four-seamer is up from 9.9 percent in 2018 to 14.4 percent this year, with the wRC+ against on it plummeting from 180 to 70. Also, as Duffey mentioned, it has allowed his breaking ball to play up, as the line against it has improved from .258/.281/.484 to .188/.240/.302.
Tyler Duffey is having a massively underrated season and has quietly been one of the better relievers in baseball the past couple of months. With as sharp as he’s looked in single inning outings the past couple of months, he’ll figure to be one of the primary arms in the Twins bullpen for October.