How Mitch Keller’s New Sinker Complements His Other Pitches

ST. PETERSBURG – Mitch Keller never threw a sinker in the minors, despite coming up during a time when seemingly every Pirates pitching prospect was getting a two-seamer pushed their way.

“The mentality in the minor leagues for us coming up was fastballs down,” said Keller.

Keller had the ability to throw his four-seam fastball down in the zone, and it got good results in the lower levels. The Pirates typically gave a pitcher a two-seam fastball if he had issues keeping the fastball in the bottom of the zone. The problem was that the Pirates weren’t focusing that pitch on the top of the zone.

“There was never a time when we were trying to throw four seam fastballs up,” said Keller. “That kind of changed when Oscar [Marin] and the new coaches came in.”

Marin, who has been the Pirates pitching coach since 2020, gave Keller the ability to elevate his four-seam fastball. Prior to this, Keller’s four seam fastball was becoming less effective in the upper levels. His ground ball rate plummeted in the majors, and his ERA was inflated.

Keller has added a sinker this year, which has helped him to work in the bottom of the zone again, with a return of his ground ball numbers. The change came after his May 13th start against the Reds.

“After the Cincinnati start, I gave up five runs, I was like alright, my fastball is getting hit, we’ve got to change something,” said Keller. “What can we do to make the fastball move more or less? Try a sinker.”

Keller had been throwing the pitch in bullpens, and it received good metrics on the Trackman. He threw the sinker for the first time in his May 18th start, and has used it 38.1% of the time — more than any other pitch — since that point.

Keller feels that the movement of the sinker is helping his four seam play better. That’s backed up by the numbers.

Prior to May 18th, Keller had a .303 average against his four seam, and a .172 ISO. Since adding the sinker as his primary pitch, the four seam fastball has a .222 average against, and no power numbers. There’s a reason for this massive change in results.

“[The sinker] gets more action [low], which is helping my four seamer [high]. Where as before it was just four seamers [high] — it’s kind of easy to look for,” Keller explained. “Now that you’ve got two separate things to look at, it makes it a little bit harder. It makes each of them play a little bit better than they would by themselves.”

The two fastballs now provide perfect complements to Keller’s breaking stuff. His four seam plays at the top of the zone, giving a high-low pairing with his curveball — a pitch he’s been throwing for 15 years. The sinker pairs with his slider, giving a horizontal split in break.

The biggest benefit of the sinker is that it is operating as a sinker should. Keller is throwing that pitch in the zone more than any of his other pitches. Opponents swing at the pitch 65% of the time when it is thrown in the zone, and make contact 90% of the time in those swings. Opponents have a .259/.386/.310 line against the pitch, giving Keller a recovery option when he’s working from behind.

“It’s huge,” said Keller after his June 24th start against the Rays. “It happened there in the fifth inning with Yandy Diaz. It was 3-0, I know I can throw two sinkers for strikes here and get back in the count and not have to worry about damage.”

Keller is seeing better control each time he uses the pitch, learning where to start it and how to throw it with more experience.

Pirates manager Derek Shelton has noticed the overall impact the pitch and the recent success has had on Keller.

“I think his mental mindset is better,” said Shelton.

Since adding the sinker, Keller has a 3.89 ERA in 34.2 innings, with a 4.12 xFIP. He’s had some poor results lately, with soft contact finding holes in Tampa, and control issues hurting him in his next start against the Nationals.

I would expect some inconsistencies as he gets used to the new pitch mix. The small sample of results is encouraging that Keller may have found the final piece needed to be a starter in the majors.


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Tim started Pirates Prospects in 2009 from his home in Virginia, which was 40 minutes from where Pedro Alvarez made his pro debut in Lynchburg. That year, the Lynchburg Hillcats won the Carolina League championship, and Pirates Prospects was born from Tim's reporting along the way. The site has grown over the years to include many more writers, and Tim has gone on to become a credentialed MLB reporter, producing Pirates Prospects each year, and will publish his 11th Prospect Guide this offseason. He has also served as the Pittsburgh Pirates correspondent for Baseball America since 2019. Behind the scenes, Tim is an avid music lover, and most of the money he gets paid to run this site goes to vinyl records.

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His ERA is over 5 and he has shown little if any improvement. Keller isn’t Tom Seaver…..more like Kip Wells actually.


He’s moved to the category where he could be a playoff starting pitcher

Now they need 3 more of them


Find it this year or don’t let the door hit you from behind…


Definitely reason for optimism.


Pulling for this kid so hard.


Pirates need him to find another gear. Just don’t believe it will happen. Hopefully I’m wrong…again.


I hope you are too. Remember, optimists are happier and live longer.

Bucs'N'Pucks (Jeff Reed)

I hope he flips a permanent switch, cause he looks like a premier case of changes organizations and goes on a tear.


Tim – did Keller just not think about pitch pairings (tunneling ?) before this season? This revelation with the 2 seamer is great, but I wonder why it took this long. And Keller had 2 prior seasons with the new pitching coach, right? So it’s not some drastically different approach this season, I assume. I’m not being critical. I’m just trying to understand the complexities beneath the surface, how the approach has evolved since 2020, and how hard this is to figure out in real life.


Separate question: why is this a make or break year for Keller? High upside arms don’t grow on trees. The only way to get an ace on a budget is to develop them. I don’t see why the Bucs wouldn’t give Keller every shot to figure it out until they actually are competing for the postseason.

And even then if Keller ends up being a competent starter but nothing more, that’s nothing to shake a stick at… and certainly a valuable asset for a contending team.


Yeah, we’ve seen that movie one too many times.


Let’s see how he does the rest of the season. My expectations for him coming into this year couldn’t have been lower. If we see much more like the last two starts, I don’t think anything has changed.

Pirates Prospects Daily



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