This story was excerpted from Martín Gallegos' A's Beat newsletter. To read the full newsletter, click here. And subscribe to get it regularly in your inbox.

OAKLAND -- Did you think Mason Miller couldn’t get any nastier on the mound? Think again.

To this point, Miller has established himself as an elite closer by relying on his triple-digit fastball (which has generated a 45.3 percent whiff rate, the highest of any Major League pitcher) and his wipeout slider. His arsenal also includes a changeup, but it’s a distant third pitch as he’s thrown it just twice through his first 20 outings.

Recently, though, the A’s flamethrowing rookie unveiled an interesting new addition to his repertoire.

While closing out a 3-0 win over the Rays on May 28 at Tropicana Field, Miller worked a quick 0-2 count on Brandon Lowe, then he unleashed a pair of pitches that registered at 97.1 and 98.1 mph. They showed up as splitters on the pitch tracker. But these were not splitters, nor were they fastballs.

They were splinkers.

You might be familiar with the splinker. It’s a pitch with a split-fingered grip that is thrown as hard as possible and dives down in the zone. Twins closer Jhoan Duran introduced it to the baseball world in 2022. Pirates rookie phenom Paul Skenes also throws a splinker, which is a hybrid between a splitter and a sinker.

Miller had been working on trying to get a feel for the splinker during his bullpen sessions in previous weeks. The three-run lead against Tampa Bay and the favorable count on Lowe gave him enough comfort to finally test it out in-game. Those were the only two splinkers Miller threw, with Lowe taking the first one for a ball before fouling off the second.

“The first one was the arm-side one,” Miller said. “Just getting to the grip in the game was a little different, so I didn’t really have it in my hand the way I wanted to. Second one was just yanked a little bit, but kind of had the movement I wanted on it. I’m just figuring out how to work that into a game consistently and smartly, too.”

Miller views his changeup as a solid third offering, but he noted that it does not generate a ton of swing-and-miss. He drew inspiration from watching Duran and Skenes throw the splinker, and he believes integrating his own can make his blazing fastball -- which carries the highest average velocity of any MLB pitcher in 2024 at 100.8 mph -- play up even more.

“I think for at-bats where a guy is fouling off a bunch of pitches or taking some close pitches, it’s just an extra wrinkle,” Miller said. “I’m sure [hitters] will game plan for it a little bit, but obviously you’re going to game plan for my bread and butter, fastball and slider. So if you add another wrinkle, I think that gives you the advantage in an at-bat.”

Asked how good Miller could be if he were to solidify the splitter as a trustworthy third pitch, A’s catcher Shea Langeliers shook his head, almost as if he was in disbelief as he pondered the possibility.

“His fastball and slider combination right now is just so dominant,” Langeliers said. “Adding a third pitch, for me, personally, I don't even know how to go about trying to hit him. He’s a really, really special pitcher. It just seems like he's built for those big moments, both mentally and stuff-wise.”

Miller acknowledged the splinker is still in somewhat of a development phase. Since debuting it, he’s pitched once after that, on Thursday, and did not throw a single splinker among his 32 pitches. For now, Miller plans to continue working on refining it before games and between appearances.

“We've talked about how we're going to use it,” Miller said. “It's kind of a work in progress. We'll see. I’ll probably go back to the drawing board on it a little bit.”