Pitcher Potpourri: Trevor Williams, Joe Ross, and Caleb Thielbar Find Homes

It’s roughly the midway point of the offseason, and things are starting to slow down. Most of the headline free agents are off the board, clearing the way for the Trevor Williamses, Joe Rosses, and Caleb Thielbars of the world to find their 2025 homes.

Those guys all signed in the final days of 2024, inking modest deals for National League clubs. Here’s a little bit about all three.

Trevor Williams Re-Signs With the Washington Nationals

Williams is a weird case. In 2023, his fastball got destroyed. That wasn’t a huge surprise — the pitch averaged 89.7 mph with just 11 inches of induced vertical break. Williams gave up 34 home runs that year; most of that damage was inflicted on his four-seamer.

In 2024, he actually lost a tick off his fastball, dropping to 88.9 mph; the movement profile was nearly identical. And yet, across his injury-shortened 66.2 innings of work, he dominated hitters with the “heater.” Williams allowed just three home runs last year; only one came off the four-seamer. The run value on the pitch went from -0.8 runs per 100 pitches in 2023 to +3.2 in 2024. What changed?

The locations, for one. While watching a random Williams start against the Orioles in May, I heard the Nationals color commentator note that the right-hander was successfully keeping hitters off balance with a mix of high and low fastballs, marking a change from his 2023 approach. The location plots, courtesy of Baseball Savant’s Pitch Highlighter tool, bear this out.

Here are all of Williams’ four-seam fastballs from 2023 located in the “shadow” zone. Note the density of pitches on the top rail and the paucity at the knees:

And here’s the same plot of shadow zone fastballs in 2024. If anything, Williams targeted the bottom of the zone with greater frequency, leaning into the pitch’s natural sinking qualities:

As I frequently write on this here website, pitches don’t exist in a vacuum. When a hitter steps to the plate, they must account for all the offerings in a pitcher’s back pocket. Increasing the usage of one pitch might therefore affect how hitters respond to another (ostensibly independent) pitch. In Williams’ case, the pitch with increased usage was his sweeper.

Williams is an extreme supinator; his fastballs average just 67% spin efficiency at a 17 degree arm angle. That motor preference lends itself to throwing breaking balls with a ton of horizontal movement, and that’s what Williams added to his game in 2024. His sweeper usage increased from 3% in 2023 to 21% in 2024, becoming his second-most used pitch after the four-seamer.

The amplification of the sweeper expanded the range of velocities and the band of horizontal movement in Williams’ overall arsenal. Hitters whiffed 47% of the time they swung at the pitch, which is a ton. But the sweeper likely had secondary effects on the fastball. Hitters could no longer sit on a couple of pitches in a tight movement and velocity window; they now had to think about the big bendy sweeper, and the fastball likely performed better as a result.

Frankly, none of these tweaks would matter much if Williams wasn’t such a gifted command artist. As I mentioned in his Top 50 Free Agent blurb, he measures as the best in baseball by Driveline’s miss distance metric, nailing targets better than any starting pitcher. Nobody threw their sweeper less frequently in the heart of the zone; by throwing his pitches where hitters can’t hurt him, Williams maximizes his low stuff profile. He’s never been a workhorse, but at two years and $14 million, the Nationals are paying sixth starter prices for someone with 80 grade command. Even with the obvious limitations, that feels like a solid bet.

Joe Ross Signs With the Philadelphia Phillies

Ross is an old fashioned low-slot sinker/slider guy, throwing those two pitches roughly 75% of the time in 2024. Against righties, the game plan is straightforward: run sinkers in on the hands, throw sliders away.

But Ross is unlikely to exclusively face right-handed hitters. The Phillies originally engaged him in contract talks with the idea that he’d slot in as their fifth starter. After the Jesús Luzardo trade, it appears that he will play more of a swingman role if all five starters remain healthy. But even with reduced responsibilities, Ross will still be expected to retire a bunch of lefties in multi-inning appearances.

In theory, lefties are a problem for Ross. In his career, he’s allowed a .353 wOBA to these opposite-handed opponents. (Righties, meanwhile, have wOBA’d just .283.) But last year, Ross had no discernible platoon split, and he achieved that platoon neutrality while using the sinker as his primary pitch to lefties.

Generally, this would be seen as a problem. In 2024, left-handed hitters as a whole hit .284 with a .441 slugging percentage against right-handed sinkers. Against Ross, they did much worse — they hit .171 off the pitch and slugged just .317.

How did Ross limit opposite-handed damage against his sinker? It wasn’t due to the movement — at roughly nine inches of induced vertical break and 13 inches of arm-side run, the pitch is basically a generic two-seam fastball. But the velocity is plus: the pitch averaged 95 mph, and Ross can run it up to 98. And when Ross hits his primary target, the pitch is basically unhittable. Or at least un-swing-at-able.

Against lefties, Ross usually targets the front hip, looking for called strikes. And when it works, it really works. Admire this backwards K to Corbin Carroll — when executed properly, that’s one of the prettiest pitches in baseball:

But the front-hip sinker is a dangerous game to play. Miss arm side just a bit, and that’s running right into the ideal left-handed swing path. The velocity gives Ross some margin for error, and he mostly got away with mistakes last season, allowing just two extra base hits off the pitch. But mistakes like this might not land so innocently in gloves this season:

Ross also occasionally targets the outer half, though he did not hit that target as successfully. And these outer-half sinkers brought him the most trouble — Pavin Smith and Jarred Kelenic both launched pitches aimed away deep into the opposite field bleachers.

Given the current state of the Phillies’ pitching depth and the size of the contract (one year, $4 million), the stakes aren’t necessarily that high. But if one of the team’s starters goes down, Ross will play a pivotal role on a club with serious championship aspirations. I have concerns that in a large sample, the platoon problems may come back to haunt him.

Caleb Thielbar Signs with the Chicago Cubs

Working our way up the arm angle scales, we now arrive at Caleb Thielbar, the left-handed reliever who inked a one-year, $2.75 million deal with the Cubs on New Years Eve.

After a run of effective seasons in Minnesota, the wheels fell off in 2024; Thielbar’s walk rate spiked, and so did his ERA. Control problems were always part of the risk profile for a pitcher like Thielbar, who throws two distinct breaking balls with enormous movement. There’s the 12-6 curveball, a somewhat expected break profile from a guy with Thielbar’s over-the-top arm angle:

And then there’s the sweeper, which is decidedly unexpected:

Landing both of those pitches in the strike zone is a tightrope walk, especially with those herky-jerky mechanics. In 2024, Thielbar fell off the tightrope, walking 11% of the hitters he saw. Double-digit walk rates and a 92 mph fastball aren’t going to cut it in a major league bullpen, but last year was the first season Thielbar really struggled with command, and the strikeouts have always been there. At the price they signed him, the Cubs are banking on him filling the lefty specialist role with aplomb. It’s a modest ambition, but it’s ambition nonetheless.