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Why did the Red Sox demote Tanner Houck despite his success?

Through his first five big league appearances, Tanner Houck is 3-1 with a 1.17 ERA, 31 strikeouts, and 10 walks in 23 innings.
Through his first five big league appearances, Tanner Houck is 3-1 with a 1.17 ERA, 31 strikeouts, and 10 walks in 23 innings.Jim Davis/Globe Staff

Through no fault of his own, Tanner Houck now resides in the borderland of the Red Sox alternate site in Worcester, biding his time while awaiting his next big league opportunity.

On the surface, the turn of events seems baffling. Through his first five big league appearances, Houck is an eye-popping 3-1 with a 1.17 ERA, 31 strikeouts, and 10 walks in 23 innings.

The Sox couldn’t have asked — or even hoped — for more. Yet with the return of Eduardo Rodriguez to the rotation, the 24-year-old righthander was redirected to Polar Park on Tuesday night.

Why? Foremost, Houck has minor league options that allow him to be shuttled to and from Worcester while the current members of the rotation (Rodriguez, Nate Eovaldi, Garrett Richards, Nick Pivetta, and Martín Pérez) do not.

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But the Sox also believe that Houck can benefit from time in the minors, just as his time at the alternate site last summer allowed him to make a sizable leap with his four-seam fastball command, playing a significant role in his big league success.

“He’s obviously performed very, very well. There’s no doubt about that,” said Sox pitching coach Dave Bush. “[But] there are a lot of factors [involved in sending him to Worcester] — his own development, our roster depth, making sure we treat him the right way. It can be tempting to really push guys fast when they’re young, come up, and do really well, but we’re also aware of his long-term development and making sure what’s right for him and for us in the future.”

In the case of Houck, as dominant as he’s been in the big leagues, debate continues about whether his arsenal will allow him to stay in the rotation and whether he can improve upon his pitch mix in a way to increase the chances of consistent success.

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He’s clearly ready to compete in the big leagues, but young pitchers often enjoy initial success before shortcomings get exposed. For instance, Clay Buchholz looked like a ready-made ace when he threw a no-hitter in his second career start in 2007. The next year, he was over-reliant on his fastball and curveball and got hit hard. The Sox demoted him multiple times in 2008 and ’09 before he established himself in the rotation.

“You can be successful here,” observed Sox manager Alex Cora, “but it doesn’t mean that you have checked all your boxes from our end. You can keep getting better.”

To this point in his big league career, Houck has relied almost exclusively on fastballs, as well as a slider. While he worked to develop a splitter in 2020, he’s barely used it, throwing it just 3 percent of the time.

“We talked a lot about trying to develop a splitter and having it function as a third pitch. For the time being, it’s not a good enough pitch to force it,” said Bush. “The fastball and breaking ball are just significantly better at this point in time, so he’s still going to overload those pitches.”

That’s not the template for a starter. Traditionally, teams have asked pitchers to develop at least three distinct offerings if they’re to go through an opposing lineup multiple times as a starter. There are, however, a small but growing number of exceptions in an era when starters are being asked to work fewer innings.

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In 2019, there were 103 starters who threw at least 2,000 pitches. Of those, three (2.9 percent) featured a mix consisting at least of 89 percent fastballs as well as one secondary pitch.

In the compressed 2020 campaign, there were 96 starters who threw at least 750 pitches (roughly the prorated equivalent of 2,000 in a full season). Of those, nine (9.4 percent) had a mix of at least 89 percent fastballs and one secondary pitch.

The pitchers who used those two-pitch mixes included some standouts. Padres hurler Dinelson Lamet threw nothing but four-seam fastballs and sliders and finished fourth in National League Cy Young voting. Lance Lynn has thrown roughly 90 percent sinkers, four-seamers, and cutters over the last two years with back-to-back top-six Cy Young finishes. Tyler Glasnow of the Rays threw almost exclusively four-seamers and curveballs last year, yet often dominated. (It’s worth noting, however, that Glasnow has reached another level in his first two starts of 2021 after adding a slider.) Rich Hill has thrown 90-95 percent four-seamers and curveballs over the last several years with significant success.

Clearly, there is room for a two-pitch starter, especially if teams are content to ask their starters to call it a day after two times through the order.

“If those two pitches are good enough, then there are certain pitchers that can make them work,” said Bush. “It’s not easy. You have to have good command and really high-quality pitches. If it’s just fastball/breaking ball, they both have to be high quality and they both have to be commanded well. It’s a tough way to survive because the hitter only has so many things to think about, but there are guys who have high enough pitch quality to do it that way.”

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Hill noted that there are ways to expand the potential of pitches so that a seemingly limited arsenal can become far more diverse. He changes speeds, locations, delivery tempos, and arm slots in order to disrupt hitters’ timing.

“If you’re a two-pitch pitcher, you can argue that it’s six different breaking balls with the same idea it’s a curveball,” said Hill. “A lot of those things go into it with two pitches and can make a pitcher successful as a starter at this level. It’s really about being more creative and having freedom to be creative.”

Houck needs a consistent delivery in order to command his mix, so he likely wouldn’t experiment with the same variables as Hill. Houck does, however, possess a four-seamer and sinker that are very different, with distinct grips, shapes, and locations (up and glove side with the four-seamer, down and arm side with the two-seamer).

Even so, because those two fastballs are roughly the same velocity, hitters can slightly narrow the number of variables they consider. Houck has nonetheless baffled hitters largely because of his unusually low release point and the movement he generates with his slider, a pitch that dives from one batter’s box to the other.

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If Houck can further develop an additional pitch to the point where he’s comfortable using it 10 or 15 times a start, then he could elevate his ceiling.

With his current mix, his slider and two fastballs are good enough that he may be an outlier who can stick in the rotation, but he’d need standout command to do so. Houck, who struggled to throw strikes in stretches in the minors, particularly against lefties, has made huge strides in locating his pitches to the point of forcing the conversation about whether he has a big league starter’s arsenal. Further command improvements or pitch development would cement his future.

“We’re still trying to develop what pitch qualities he has and what he ends up being. I don’t know what it’s going to look like right now,” said Bush. “He’s not a finished product.”

Nonetheless, Houck already represents the organization’s most successful homegrown starter in years and a trusted source of big league-ready depth.

“Whenever we need him,” said Cora, “he’ll be here and he’ll perform.”

Who needs a third pitch? Of the 96 major league starters in 2020 who threw at least 750 pitches, nine (9.4 percent) threw almost exclusively fastballs and one additional pitch. * - Houck threw 265 pitches in 2020.
Pitcher Fastball(s) and primary off-speed or breaking ball Usage (%) Other pitch(es) Usage (%) Performance
Dinelson Lamet Four-seam fastball, slider 100.0 None 0.0 3-1, 2.09 ERA, 12.1 K/9
Brad Keller Four-seam fastball, sinker, slider 98.0 Changeup 2.0 5-3, 2.47 ERA, 5.8 K/9
Tyler Glasnow Four-seam, curveball 95.4 Changeup 4.7 5-1, 4.08 ERA, 14.3 K/9
Brady Singer Sinker, slider 94.5 Changeup 4.7 4-5, 4.06 ERA, 8.5 K/9
Garrett Richards Four-seam, sinker, slider 92.5 Curveball 7.5 2-2, 4.03 ERA, 8.1 K/9
Patrick Corbin Four-seam, sinker, slider 92.3 Changeup 7.7 2-7, 4.66 ERA, 8.2 K/9
Lance Lynn Four-seam fastball, sinker, cutter 90.5 Curveball 9.5 6-3, 3.32 ERA, 9.5 K/9
Framber Valdez Four-seam, sinker, curveball 90.3 Changeup 9.7 5-3, 3.57 ERA, 9.7 K/9
Chris Paddack Four-seam, changeup 89.2 Curveball 10.8 4-5, 4.73 ERA, 8.8 K/9
Tanner Houck* Four-seam fastball, sinker, slider 97.0 Splitter 3.0 3-0, 0.53 ERA, 11.0 K/9
SOURCE: MLB.com, Baseball-Reference.com

Alex Speier can be reached at alex.speier@globe.com. Follow him on Twitter at @alexspeier.