Baseball is a game of adjustments. Sometimes it feels like no one adjusts more than Danny Duffy. One game, he has a windup. The next, he’s working exclusively with a slide-step. Sometimes, he’ll set up in the middle of the rubber. Other times, he can be found working more toward the third base side. At times, he thought he was tipping pitches, so more tweaks to his delivery were made. Sometimes he breathes through his eyelids… You get the point.
It’s not just mechanics for Duffy. It’s also the pitches he features. He generally throws what could be considered a standard array for a starting pitcher: Fastball, sinker, curve, slider, change. But, given the game and the year, his usage is constantly changing. Sometimes it works. Sometimes it doesn’t.
With Duffy set to make his third Opening Day start, that leaves us guessing as to the type of pitcher we will see over the shortened schedule this summer.
Brooks Baseball has a detailed breakdown of Duffy’s pitches. I’ve chosen to focus on the last four years, starting in 2016 for a couple of reasons. One, the 2016 season was arguably the best of his career. And two, it was the last time he pitched out of the bullpen so we have a largely uninterrupted set of data with him in the rotation, which is where he will be for this season.
It’s an interesting look at how a particular pitch can be in favor, and then seemingly fall out of said favor over the course of a few seasons.
I’ll refer to this chart in discussing Duffy’s pitch selection. It’s important to note that the first two months of 2016, Duffy pitched in the bullpen prior to transitioning to the rotation at the end of May. He was shutdown early in 2018, making just a single start in September. And last year he made just one start in April and missed all but one start in August. Obviously, those percentages in those months will be skewed.
Duffy started experimenting with a curve in June of 2018. By July, he was feeling good with the results. It’s a pitch that features above-average drop—roughly four to five inches—with below-average lateral movement. This was certainly a notable development. Duffy hadn’t thrown the curve much at all since 2014. Duffy spoke to The Athletic about rediscovering an old pitch.
What I was doing wasn’t working. So I tried to figure something new out. This isn’t so new, as it is trying to rekindle what I had when I first came up…I was afraid to throw it. That was the pitch that I ultimately blew out my elbow on. (It was) a mental block a little bit.
The curve was a massively successful offering for Duffy once he started throwing it in 2018. He featured it to both left and right-handed batters with generally the same frequency, and would unleash it roughly 16 percent of the time when he was ahead in the count. It was enough to keep hitters off balance. He limited the opposition to a .213 batting average and .263 slugging percentage on the curve that summer. He didn’t allow a single dinger on the pitch.
In 2019, something changed. He featured the curve a little less overall in favor of another pitch (more on that in a moment) but still threw it around 12 percent of the time when he was ahead in the count. But hitters weren’t fooled. They hit .333 against the curve with a slugging percentage of .410. Again, he didn’t allow a homer off the curve, but the hits were dropping like they hadn’t the previous year.
By September, the curve completely fell out of favor.
It looks like Duffy was fiddling with the release point of the pitch. His arm slot was ever so slightly higher in 2019.
The cluster that moves over to the left in 2019 are curves Duffy threw in September. He’s always trying to find something that works.
The result of the slightly higher release point can be seen in the heat map from Duffy’s curves. The pitch lacked bite and stayed elevated in the zone.
No wonder batters feasted on this pitch in 2019. And no wonder Duffy scrapped it as the season evolved.
When Duffy was working out of the bullpen, he would lean on the slider and the change as his secondary pitches. Both pitches stayed in the arsenal when he moved back to the rotation, but he really seemed to lean on the slider. It was the pitch he threw more than any other (fastball included) in 2017. That year he finished with a 3.81 ERA and a 3.2 SO/BB ratio, his best rate working in the rotation. Batters hit just .241 against the slider in ’17 with a .312 slugging percentage.
But the slider started getting hit. Hard. In 2018 opponents hit .296 with a .574 slugging percentage against it. Duffy started moving away from the pitch in June. By July, he was offering it less than 10 percent of the time.
But when Duffy rejoined the team in late April of 2019 after about of shoulder soreness, so too did the slider. As the season unfolded, it was the pitch that largely replaced the curve. He spoke to the Kansas City Star about what he was trying to do with the pitch.
I started working on it when I started throwing again in spring training after the boys broke camp. I’m just trying to stay behind it a little bit longer and make it come out of fastball plane. It’s been really effective for me when I’ve located it.
The aim of the slider in 2019 was to travel along the fastball plane and to feature less vertical break. The curve that had played an increased role at the end of 2018 was to be the pitch that would feature the downward plane, the slider was to move laterally. On that basis, the pitch worked. Duffy’s slider which had averaged 2.3 inches of vertical break in 2017 and 2018, featured just 0.3 inches of drop in 2019. But the pitch also lost horizontal break, going from 7.2 inches in 2017 to 4.6 inches in 2018 down to 3.1 inches in 2019.
When it comes to spin rate, Duffy’s slider is about as consistent as you can get.
2017 - 2313 rpm
2018 - 2330 rpm
2019 - 2310 rpm
The results were a mixed bag. The opposition hit just .239 against the pitch last year, but slugged .479. It got so bad with the slider at one point Duffy surrendered six home runs in three starts spanning late June and early July off that pitch.
The changeup is a pitch Duffy threw roughly 20 percent of the time since returning to the rotation in 2016 up until 2018. But when the lid lifted on the the 2019 season, Duffy was featuring the pitch less than half that.
But the suppression of the change lasted about three months. By July, his percentage of that pitch was increasing steadily. By September, thanks to a mechanical adjustment, he told MLB.com that he was once again believing in the pitch.
But with the move toward the third-base side of the rubber, Duffy has again found conviction in his changeup. “Once I came off the [injured list], Cal and Vance made that change for me and it’s made a world of difference. Really, all the credit goes to them. It has given my changeup more room to work. Just something that minor can make all the difference.”
The move paid off. In September, Duffy held the opposition to a .154 batting average when a plate appearance ended on a change. It’s not a put-away pitch for Duffy, rather it’s one he will turn to when he falls behind in the count, although he will certainly use it when ahead.
What to expect in 2020
For Duffy, it’s an annual rite of Spring Training to detail what he did differently that offseason to prepare for his starts. Ahead of the 2019 season, he talked about how he tried to build strength in his left shoulder and his core. This year, he started his winter throwing program earlier and was reaping the benefits of being so far ahead of batters early in spring. (At least before the camps were shut down.)
It’s a 60 game sprint as they say, so Duffy will get about 12 starts over the course of these two months. He’s in strong shape and won’t need to worry about pacing himself over the grind of a 162 game season and 32-odd starts. It will also make it difficult to identify the trends if Duffy starts to alter the arsenal.
Everything points to Duffy leaning on the slider and change as secondary weapons of choice. For now, the curve will continue to play a reduced role. But don’t be surprised if the pitch usage is once again dramatically different by the time the Royals reach the finish line.