Pirates prospect's spring debut features pitch graded literally off the charts

Spring training is a time for players to work on new things, make adjustments, and for prospects to put themselves on the map against better competition. It's also a time when fans often get their first good look at prospects who have yet to debut on the MLB stage.

The Pirates have gotten some of their more exciting young arms into Grapefruit League action already, and one such pitcher has already entrenched himself into "oh my gosh, this guy is nasty," eyes-wide-open-emoji territory. It wasn't Paul Skenes. It wasn't Jared Jones or Bubba Chandler, either.

Enter Thomas Harrington.

Pirates' Thomas Harrington burst onto the scene with a filthy breaking ball in his spring debut.

The Pirates drafted Harrington out of Campbell with a competitive balance draft pick at the end of the first round in 2022. He has a career minor league ERA of 3.09 across four levels. He split most of the 2024 season between Double-A Altoona and Triple-A Indianapolis, posting a cumulative ERA of 2.68 and recording a sub-1.00 WHIP at each level.

Generally lauded for his deep arsenal and 60-grade command (he has a 6.1% walk rate as a pro), Harrington doesn't boast the jaw-dropping swing-and-miss stuff like many other top-100 prospects do. He's your classic, old-fashioned "change speeds and keep them guessing" pitcher.

That's what made his spring debut on Monday against the Braves even more eye-opening. The phrase "off the charts" is typically used to exaggerate something that enjoys success or exceeds expectations. But according to X user Pitch Profiler, Harrington's slider was, in the most literal sense, off the charts:

Stuff+ is a metric designed to show how nasty a pitch is based solely on its physical characteristics. Like other "plus" statistics, 100 is the league average, and a number higher or lower than 100 dictates separation from the league average. Harrington's slider (more accurately categorized as a sweeper by Baseball Savant) generated a Stuff+ score of 164. If that seems ridiculous, that's because it is.

No pitcher who topped even two innings pitched in 2024 threw any pitch that reached a Stuff+ score of 164. The closest competitor was Emmanuel Clase's slider; he threw the pitch 202 times, allowing just a .145 batting average with one extra-base hit (a double) and a whiff rate over 35%. The Stuff+ on that pitch was 156, eight points behind what Harrington managed on Monday.

No, this doesn't necessarily mean that Harrington is destined for stardom or will start striking hitters out at a Paul Skenes-like pace. But the fact that he's boasting stuff of this caliber in February is pretty significant. Eyes will now be glued to all of Harrington's outings for the rest of the spring. While he's unlikely to find himself in the Pirates' Opening Day rotation, he could be a force on a big league mound sooner than people think.