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Seranthony Dominguez and a weird 2023 season

Just what in the heck happened?

Championship Series - Philadelphia Phillies v Arizona Diamondbacks - Game Four Photo by Sean M. Haffey/Getty Images

Sometimes, players that are the keys to a team’s season aren’t the ones you would expect them to be. Looking at the Phillies as they embark on the 2024 campaign, it’s easy to point at players like Bryce Harper and Kyle Schwarber and Zack Wheeler and call them the most important players because they are the stars. They are the ones being compensated accordingly, expected to produce over the full 162 game season. That’s true of any team - the stars need to produce like stars if a playoff berth is to be gained.

There are always other players, though, that would have to perform well for an additional step to be taken. These are the players that teams plan on being better than before that would give a little security to their manager. One of those players for the Phillies in 2024 might be Seranthony Dominguez. The dominant reliever that was a buzzsaw through the 2022 playoffs never really felt present in the following season. It always felt a little hairy whenever Dominguez took the mound. The question becomes: why?


Trying to figure out what went wrong with a pitcher is a multilayered journey. You have to look at a number of different things and ask a number of different questions. What his stuff different? Were there monumental changes to his rate stats? Did he struggle to throw strikes and if not, were the strikes he threw good ones or bad (i.e. did he struggle with command)? Was his arm slot different than in years past? Was he tipping pitches? It takes a while to break down and often, there is no simple answer. Going on this journey through Dominguez’s 2023 season, a few things jumped out as somewhat off.

Anyone who is anyone is going to start at Baseball Savant. What do those percentile ranks look like? Usually there is an answer there, so let’s compare the two seasons.

Well now. It probably becomes pretty obvious where the changes were. There is almost a night and day difference between several important categories. In 2022, Dominguez was able have top notch whiff rates and strikeout rates, but when hitters made contact, they hit the ball hard. In 2023, these things flip flopped. Hitters didn’t make anywhere near as hard of contact, but they also weren’t whiffing on pitches and consequently, the strikeout rate dropped. It makes you wonder if there was a concerted emphasis on this from the team’s perspective, to have Dominguez give up less hard contact at the cost of having hitters whiff less often. In the perfect world, both would be the desired outcome, but as you can see, that did not happen.

The next step is going through his rate stats, where the big difference is he actually lowered his walk rate....but again as we saw in the percentiles, he didn’t strike out as many batters. The walk rate dropped from 10.6% to 9.8%, not a huge drop, but a drop nonetheless. He didn’t keep the ball on the ground as much as he did in 2023 and when the ball was in the air, it left the park a bit more often. That might explain the ERA jumping almost a full run....except it wasn’t a crazy, out of control difference. He only gave up three more home runs than the year before, which when you only throw 50 innings a season, makes a difference in ERA.

It led me to look at his stuff a little more and something felt a little different. Let me show you two different pitches of Dominguez’s.

I chose both of these pitches because they are both utilizing (roughly) the same camera angle that will emphasize what I found to be a little different about Dominguez. The pitch in both is a slider in about the same part of the zone. Both of these pitches occurred in 2023 and have the same kind of movement despite being months apart.

Now, the next two are two more sliders.

These are three more sliders from Dominguez from the 2022 playoffs when he was at his nastiest and was near untouchable (I know I said two more, but that one to Mancini is just filthy). They’re not quite in the same part of the strikezone as the examples I showed from 2023, but the picture should be a bit clearer when comparing the two sliders in two years.

To my untrained eye, there is a difference in the horizontal movement of the pitches. The one from 2022 looks much tighter in its left to right movement while the slider from 2023 has more closely resembles something of a sweeper, “sweeping” across the strikezone against Andrew Monasterio. Is there evidence to back that up?

Using Baseball Savant, we can determine just that thing and...

Well that’s not right. How can Dominguez’s slider look so much sweeper-y in 2023 than it did in 2022? Are my eyes playing tricks on me? According to the data - yes. Statcast says the slider is moving less horizontally than it ever has and that I am a fool and a liar.

*This is heading down a rabbit trail, but Dominguez’s slider data (horizontal and vertical movement) closely resemble the data of Zack Wheeler’s cutter, so much so that I think the pitch should be reclassified, but that’s for smarter people to determine than I.

So it wasn’t the slider that was off. Was it a different pitch? His fastball got K-I-L-T KILT at a much higher rate than before as evidenced by the differences in BA and SLG on the pitch (.222/.361 in 2023 vs. .161/.268 in 2022) so that’s probably a lot of it as well.

So what we’ve got so far is that:

  • his slider looked different in 2023, but it wasn’t
  • his fastball got hit for base hits more often
  • he didn’t get his as hard as he did in 2022, but...
  • he also didn’t strike out as many people

See, that’s a weird year for a pitcher like Dominguez. Judging off of memory and subjective thinking, it sure felt like he was getting hit harder more often than he actually was, something we now know to be false. So that leads to more questions, right?

Well, not really.

Looking at all the underlying data can be helpful and useful and all that good stuff, but it kind of looks like Dominguez’s struggles can be boiled down to the age old issue: don’t leave your stuff over the middle of the plate.

Utilizing Baseball Savant’s zone breakdown, we can see the difference in seasons when it comes to what Dominguez was doing. In 2022, he was quite effective, even with pitches that were left in the zone.

In 2023, that same effectiveness didn’t seem to exist or happen as frequently, which is probably the primary culprit for the struggles he had in 2023.

It’s just worse all the way around for Dominguez. In order to be better in 2023, this is going to have to change.

Dominguez is a big part of the team’s bullpen plans. As much as we want to say he was so good in 2022, there was a month there at the end where he was near unpitchable at times. The stuff he did show prior to that month, he was excellent. If he can get back to that kind of dominance back to being then norm, that’s another weapon the team can deploy at the end of games. It’s one of the things they’ll be working on throughout the season.