When Matt Waldron made his major league debut for the Padres last June 24, it was a noteworthy event. While a few position players had thrown the occasional knuckleball ast a goof after taking the mound for mop-up duty, no true pitcher had thrown one in a regular season game in two years. The last one who had done so, the Orioles’ Mickey Jannis, made just one major league appearance. Mixing his knuckler in with four other offerings, Waldron bounced between the minors and majors for a couple months before sticking around in September. Now he’s a regular part of the Padres’ rotation, and he’s having success… some of the time.

Through six starts totaling 31 innings this season, Waldron owns a 4.35 ERA (111 ERA-) and 4.06 FIP (103 FIP-), which won’t put him in contention for the Cy Young award but is respectable enough to keep him occupying a back-of-the-rotation spot. For what it’s worth, within the Padres’ rotation he’s handily outpitched both Michael King (5.00 ERA, 6.30 FIP), whom the Padres acquired from the Yankees as one of the key pieces in the Juan Soto trade, and Joe Musgrove (6.94 ERA, 6.59 FIP), who last year signed a $100 million extension.

Waldron is striking out a modest 19.7% of hitters but walking just 7.3%; his 12.4% strikeout-walk differential is second best among Padres starters behind only Dylan Cease’s 18.7%, and Waldron’s 1.16 homers per nine sits in the middle of the pack among their starting five (which also includes Yu Darvish) — and a vast improvement on his 1.67 allowed per nine at Triple-A El Paso in 2022–23. He’s done a very good job of limiting hard contact, with his 87 mph average exit velocity placing in the 78th percentile and his 33.3% hard-hit rate in the 75th percentile.

For those unfamiliar with Waldron’s back story, Cleveland drafted him out of the University of Nebraska in the 18th round in 2019, then sent him to San Diego as the player to be named later in the Mike Clevinger-for-Josh Naylor blockbuster in November 2020. The following spring, Waldron caught the Padres’ attention by throwing a knuckleball in warm-ups; he and his twin brother Mike had figured out how to throw the pitch way back in little league. The Padres encouraged Waldron to feature the pitch, and remained patient with him as he took his lumps. In 2022, he was hit for a 6.26 ERA and 5.05 FIP in 113.2 innings at Double-A San Antonio and at El Paso while throwing the pitch 9% of the time.

Last year with El Paso, Waldron threw the knuckleball about 22% of the time before first being called up in June. He was rocked for a 7.31 ERA and 5.44 FIP in 92.1 innings total innings at Triple-A; he improved his strikeout rate from 18.8% in 2022 to 23.8% in ’23, but also served up 1.75 homers per nine. Obviously, those aren’t good numbers, but it’s worth remembering that altitude is a significant factor in the Pacific Coast League, not only in El Paso, where the Chihuahuas’ Southwest University Park is 3,750 feet above sea level, but also in Albuquerque (5,100 feet), Reno (4,500 feet), Salt Lake City (4,230 feet), and Las Vegas (3,000 feet). Batted balls carry further at such altitudes than at sea level, and knuckleballs also move less.

Had Waldron been hit as hard in the majors as he was in the minors, he wouldn’t have lasted long. But while he did turn in some clunkers, he allowed just five runs in 17 innings over his final three outings against the A’s, Cardinals, and Giants — not exactly offensive juggernauts, but major league teams nonetheless. He finished the 2023 season with a 4.35 ERA (105 ERA-) and 5.46 FIP (126 ERA-) in 41.1 innings.

In the majors last year Waldron threw the knuckler 26.7% of the time, but this season, he’s up to 35.4%. Already he’s become just the sixth hurler of the pitch-tracking era — that is, since 2008 — to throw at least 100 knuckleballs, though he’s the first to get to that point while throwing the pitch less than two-thirds of the time. Thanks to Statcast, we know that the 27-year-old righty throws the pitch about as hard as R.A. Dickey, the last prominent knuckleballer.

Aside from Wright’s last gasp — 6.1 innings sandwiched between an 80-game PED suspension and a toe contusion, followed by Tommy John surgery — the only other pitcher to throw at least 50 knuckleballs in the majors over the last half-decade was Ryan Feierabend, who made two appearances for a total of 5.2 innings with the Blue Jays in 2019. From this group, Waldron’s knuckler is the first for which we have direct measures of spin thanks to the upgrade from the radar-based Trackman system to the optical-based Hawk-Eye system, which happened in 2020. For the games that we have such data — all but Waldron’s first two starts of this season — he’s averaged 276 RPM with the pitch. If I’ve done my math right, and that’s a load-bearing if, that translates to about 2.2 revolutions of the ball between his release point and the plate. According to physicist Alan Nathan, who was crunching the numbers using Trackman, Dickey’s knuckler was on the order of 150 RPM, which translates to about 1.5 revolutions between release and home plate.

With less reliance upon the knuckler, Waldron comes to the table with a more complete arsenal that includes both a four-seamer and a sinker, as well as a sweeper and a cutter. His mix varies depending upon the batter’s handedness:

Our pitch modeling metrics don’t grade Waldron’s knuckleball — they don’t have any real basis of comparison — and don’t think much of his other offerings save for his sweeper, which is graded as a slider by both Stuff+ and PitchingBot. The models do appreciate his command:

The fringy nature of Waldron’s non-knuckleball pitches is somewhat secondary to the element of unpredictability. Most hitters haven’t faced the fluttering pitch before, and its speed and movement contrast greatly with his other offerings — though ideally, he throws the knuckleball so that it mimics the early path of his fastballs. “I use it coming out that same tunnel,” he said after his debut last year.

This year, Waldron is throwing the knuckler on the first pitch of a plate appearance 42% of the time, with the four-seamer and sweeper both at 22.6%, the sinker at 16.8%, and the cutter at 7.3%. When he’s ahead in the count, his usage of the knuckler rises to 48.1% (58.1% against lefties, 38.8% against righties), and when he’s behind it falls to 16.3% (15.9% for lefties, 16.7% for righties), with the sweeper (25%), sinker (23.3%) and four-seamer (20.9%) all pretty equally distributed.

Batters hit .242 and slugged .485 against Waldron’s knuckleball last year; this season, he’s held them to a .163 AVG and .302 SLG against it, and his whiff rate has increased from 24.7% to 25.8%. He’s faring better with his four-seamer than he did last year (.259 AVG/.519 SLG in 2023, .231 AVG/.346 SLG in ’24), with whiff rates in the 21% range for both seasons, but his other pitches have been knocked around. Lefties are hitting .259/.344/.444 (.350 wOBA) against him, righties .254/.280/.394 (.294 wOBA).

Waldron’s past two starts have put the good, the bad, and the ugly on display. Last Wednesday, he authored one of the best starts of his brief career — and at Coors Field, no less. Throwing 30 knucklers and 91 total pitches, he held the Rockies to four hits, three walks, and one run over six innings while striking out five. He retired the first 10 hitters he faced before a pair of walks and a single loaded the bases with one out in the fourth, but pitched his way out of trouble. After stranding one runner in the fifth, he served up a solo homer to Ryan McMahon with one out in the sixth, but by that point the Padres had provided Waldron a 5-0 lead. With two outs, Waldron walked Elehuris Montero and yielded a single to Brenton Doyle, but he got Brendan Rodgers to ground out and escaped the jam. That ended his night, and a trio of relievers closed things out for a 5-2 victory.

The Rockies went 0-for-7 against Waldron’s knuckler, whiffing on six out of 15 swings; two of those were for strike three, to Charlie Blackmon and Ezequiel Tovar, in the first inning. Waldron generated a 33% called strike and whiff rate (CSW%) both with the knuckler and overall. The five knuckleballs put into play had an average exit velocity of 85.3 mph; two of them were hard hit but none were barreled, while the other three had exit velos between 71 and 80 mph. As for the rest of Waldron’s offerings, he threw the sweeper 26% of the time, four-seamer 21%, the sinker 12%, and the cutter 8%. McMahon’s homer came off a sweeper, as did a Rodgers single; two other singles were off sinkers. Of the other strikeouts, he caught two hitters looking at sinkers (one on a pitch that was well outside the zone) and blew a high 89-mph four-seamer by Tovar.

Afterward, manager Mike Shildt praised Waldron for carving out a spot in the rotation and for reaching the six-inning mark for the second time in his career. Via Dennis Linn of The Athletic:

“He’s established himself as a starter,” Shildt said. “He’s shown the ability to pitch deep in games and give teams a chance. Regardless of repertoire, if you’re going to start, that’s going to be a big part of the prerequisite for being able to do that … and he just happens to have a knuckleball that’s part of his arsenal. That’s the biggest thing for me. Whatever your pitches are, they are. However you get there, you get there. But being able to get there and get a solid six innings and buy your team a chance to win baseball games is ultimately the prerequisite, and he’s been able to do that.”

While Waldron worked six innings again on Monday night in San Diego against the Reds, he had a much rougher time. He began his evening in style, striking out Will Benson on three pitches, the last of them was his first knuckleball of the night. But after getting ahead of Elly De La Cruz with two more knucklers (one a whiff, the other a foul ball), he left a sinker high in the zone, and it got absolutely crushed, 113.4 mph off the bat and 443 feet into the left center field seats. Oops.

Matt Waldron, Gorgeous Knuckleball.

179 RPMs pic.twitter.com/0FNJgBgycf

— Rob Friedman (@PitchingNinja) April 30, 2024

Waldron struck out Jake Fraley on a knuckleball to end the first, but in the second he was touched up for a pair of runs. He allowed two hits on a pair of hard-hit balls, Nick Martini’s 100.5-mph single to right off a middle-middle knuckler, and Jeimer Candelario’s 99.7-mph double to left center off a sweeper that was low and away. Santiago Espinal’s sacrifice fly — a hard-hit ball to the warning track — scored Martini, and then Waldron was called for a balk, bringing home Candelario. The third inning brought even more trouble, as Benson and Spencer Steer each rocketed doubles, the former off a cutter on the inner third of the plate, the latter off a knuckler right at the bottom of the zone.

Down 4-1 by this point, Waldron settled down and turned in three scoreless innings, getting De La Cruz to chase a knuckler below the zone for a strikeout after allowing another double to Benson, whom he then picked off second to end the frame. For the night, Waldron finished with six hits and four runs allowed; he didn’t walk anybody and struck out four, all on knuckleballs (two looking, two chasing low). He generated just four whiffs and a 19% CSW% with the knuckler, and got just one whiff against his other pitches en route to a 24% CSW% overall. He gave up a season-high eight hard-hit balls, compared to five against Colorado.

It wasn’t a banner night for Waldron or the Padres, who were dominated by Nick Lodolo. The 26-year-old righty allowed just one hit, a leadoff homer by Jurickson Profar, and struck out 11 over seven innings, sending the Padres to a 5-2 loss, their fifth straight defeat. Even so, while Waldron remains very much a work in progress, it’s great to have a real live knuckleballer working regularly in the majors again.

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