Should We Expect Tanner Houck To Come Back Down to Earth in 2025?

Tanner Houck was the shining star of the 2024 Red Sox pitching staff, putting up a 3.12 ERA after running a 5.01 ERA in 2023. When he stepped to the mound every five days, you knew he was more likely than not to turn in a solid pitching performance. Even as he began to break down toward the end of the season, he could be counted on to eat innings and help preserve an already overworked bullpen. It's fair to say that few of us saw this season coming. Before the season began, the question was whether Houck should be in the bullpen because he couldn’t be trusted to go deep into games, and letting him see the opposing lineup for a third time would spell disaster. He proved everyone wrong and turned in the best season of his career. Now we have a question to answer: how much should we trust Houck’s breakout performance? Let’s dive into some numbers.

First, Houck didn't just improve his ERA. His strikeout rate fell a bit, but his walk rate fell by much more. The advanced ERA estimators felt that Houck had been a bit unlucky in 2023, so he was probably due for a bit of regression anyway. Even so, all of those advanced metrics liked him better in 2024. He knocked more than a run off his FIP and nearly half a run off his xFIP. That's a good sign. That's not to say that Houck didn't get a least a little bit lucky. His home run per fly ball rate dropped by nearly half, going from one of the highest in the league in 2023 to one of the lowest in the league in 2024. That's not usually a very consistent indicator, so we should expect Houck to give up a few more home runs next season regardless of what happens.

Next, we should step back and look at the big picture, because Houck was a completely different pitcher this season. In 2023, he threw a four-seam fastball 10% of the time and a cutter 11% of the time. In 2024, he completely scrapped both of those pitches and threw his splitter more than twice as often, leading with it against left-handed batters. He also made some mechanical changes; he raised his arm angle and got much less extension. Houck has always struggled against lefties, but he was better in 2024, and steeper arm angles are known to be more effective against opposite-handed batters. The effect on his pitches was dramatic. He traded his true slider for a sweeper with more than five extra inches of horizontal break, yet somehow the pitch barely lost any horizontal break or velocity. That's not normally how these things work. The splitter added nearly four inches of drop, and the pitch modeling metric Stuff+ went from absolutely hating it in 2023 to thinking it was Houck's best pitch in 2024. The splitter got hit a bit harder this season, but its average launch angle dropped from 5 degrees to -5 degrees. The splitter wasn’t his strikeout pitch — that honor still belonged to his sinker — but it was an effective out pitch. All batters could do with it was beat it into the ground. Houck's sinker actually lost a little bit of sink, but look at the difference between his pitch movement charts.

Houck was all about East-West movement in 2024. Generally speaking, vertical break is better for racking up whiffs, while horizontal break is better for inducing soft contact, and that's exactly how things played out for Houck. His whiff rate fell a huge amount, from 28.8% to 22.6%, but his average exit velocity and hard-hit rate fell too. He also earned a ton more called strikes, so his CSW% (or called strike and whiff rate) was actually higher this season. So Houck earned fewer whiffs, but he still ended up with more strikes and softer contact. His 55.5% groundball rate was among the highest in the league. More strikes, weaker contact, and more groundballs is an excellent recipe for success, even if it means sacrificing some swing-and-miss.

Knowing all this, let's address our original question: Can we trust that Houck's breakout will continue into 2025? Obviously, we shouldn't expect him to keep dodging home runs forever, and pitchers who specialize in avoiding hard contact are prone to more ups and downs than pitchers who rack up big strikeout totals, but there's a lot here to be excited about. These are big changes to his mechanics, his pitch mix, and his movement, and there's no reason that those things should suddenly disappear in 2024. I think it’s entirely possible that 2024 was the first in a long run of successful seasons for Houck. He proved throughout very nearly an entire season that he has the ability to mix his pitches, vary his speeds and locations, and go deep into games when needed. So far, he has been the shining star of the Bailey Pitching Lab, and there's no glaring reason to expect him to come down to earth next season. Currently, Houck should be sitting second in the rotation behind newly acquired front-line starter Garrett Crochet, but don’t be shocked to see a discussion about who starts Game 1 of a playoff series. If the improved rotation is any indication, that's where they'll be, and they'll be able to trust Tanner Houck’s breakout 2024 to carry over into a dominant 2025.