Often when a pitcher moves to the bullpen, his repertoire changes. Lesser offerings are eliminated as shorter outings typically mean that the pitcher will face an individual hitter just once in a game, and thus giving the batter multiple looks isn’t as necessary. The shorter outings also means that stamina is no longer a factor and the pitcher often will throw harder thanks to giving maximum effort on every pitch instead of going at 90-95% to sustain velocity for 100 pitches. This is why former starters such as Wade Davis and Andrew Miller have suddenly become some of the best relievers in MLB.
Tyler Duffey is currently undergoing a similar renaissance, where he’s not necessarily on their same level but he’s already become the Twins’ most talented reliever on the roster. However, Duffey is evolving in a different way than most pitchers that underwent the same transition.
Yes, Duffey is throwing harder. His underwhelming 90 MPH fastball has become a more-acceptable 92 MPH. The curveball is up 1 MPH and his change-up is slightly faster as well. He has changed his pitch usage as well, but here’s where he’s straying from the norm. As I mentioned before, pitchers moving to the bullpen often eliminate one or two lesser pitches. For Duffey, this would be his change-up. Instead, Duffey is throwing it just as often, as it was used about 5.6% of the time as a starter in 2015-2016 while it has only dropped to 5.2% this year.
Your second guess might be to expect that Duffey has leaned even more on his curveball. After all, it was his best pitch as a starter and he would use it more often than his four-seam and two-seam fastballs. But that’s not the case, either, as Duffey is also throwing his curveball about as often as he did in the past. As a starter, it was utilized about 39% of the time; as a reliever, that number is 36%.
It turns out the biggest difference Duffey has made with his repertoire is with the fastball. As a starter, Duffey used his four-seamer a little more than the two-seamer, as the usages came in at 30% versus 23% (despite the suggestion that he also threw a cutter, we never had any evidence of the pitch existing at Inside Edge).
This season, Duffey has turned the two-seamer into his primary pitch while significantly reducing the usage of his four-seam fastball. Unfortunately, it hasn’t led to a significant increase in his groundball rate, though (49.4% this year, 48.5% for his career).
That’s not the only way Duffey has changed his pitches, though. The changes between the following two plots should be pretty obvious.
The added “rise” on the fastball would normally be noteworthy, but anecdotally I’ve seen that many pitchers are getting more “rise” on the ball than in the past and I wonder if that’s not a byproduct of MLB switching from pitchF/X to MLB Advanced Media (read: Statcast) data this season. I’d rather focus on the curveball movement instead. In the past, Duffey would vary the shape of his curveball, alternating between a 12-to-6 offering and a sweeping breaker that had a little more drop. This year, Duffey has essentially eliminated the sweeper. I don’t have the expertise to fully know why the 12-to-6 would be more beneficial than the sweeping curve, but my best guess is that the straight hook doesn’t stay on the same plane with the bat’s swing as long as the sweeping breaker does.
The final change we’ve seen in Duffey has to do with his placement on the pitching rubber. As a starter, Duffey would stay on the first base side of the rubber regardless of the hitter (screenshots from Aug. 8th, 2016).
Meanwhile, as a reliever, he has shifted depending on the batter’s handedness (from April 17th, 2017).
This might explain why Duffey stopped throwing his sweeping breaking ball. By moving a little more to the third base side of the rubber, Duffey increased the angle he throws towards home plate, thus he didn’t need to manufacture that angle by throwing a different curveball. I have no idea, I’m just spitballing here.
Regardless, Duffey has made multiple changes as he transitioned from the rotation to the bullpen and it has made him into the best reliever in the bullpen. It will be interesting to see if he earns more of a setup role with Paul Molitor as the season continues.