Behind Teng Kai-Wei's Sweeper: The MLB Player Development Revolution

Central News Agency

By Lin Hong-han, Central News Agency Correspondent in Los Angeles

2026/6/11 10:24 (Updated 6/11 10:41)

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Data and imagery not only dominate training but have also become a common language on the field, putting many old-school baseball people who rely solely on experience and feel out of work. Some call it a modern-day 'Moneyball,' while others refer to it as the 'Player Development Revolution.'

Taiwan's new-generation MLB pitcher, Teng Kai-Wei, is a representative figure who has risen under this wave. From the San Francisco Giants to the Houston Astros, Teng's progress at each stage is inseparable from the mainstream training methods of the modern MLB.

Teng learned to coexist with technology early on. During his time in the lower minor leagues in 2018 and 2019, he made it a habit to study opposing lineups on a computer before games, slow down video to observe swing trajectories, and identify weaknesses. That year, he posted a 7-0 record with a 1.58 ERA in Single-A.

Before officially moving to the US, he experienced American-style training at the 'Texas Baseball Farm' in 2016, the same training facility that once helped Chien-Ming Wang make a comeback. Teng realized that the American approach of using equipment to improve pitching mechanics and prevent injuries was very different from the traditional heavy workload pitching in Taiwan.

After joining the Giants organization, Teng benefited from the sports analysis team, developing sharper breaking balls. In the past, pitchers mostly relied on feel to develop a weapon pitch, spending a lot of time without necessarily finding an answer. But in the age of science, as soon as a ball is thrown, various detailed data can be seen on a computer, allowing for immediate adjustments to the release.

Not only did the team have a science team, but during his time with the Giants, Teng also attended the independent training facility 'Tread Athletics' during the off-season to absorb the latest information. He brought this background to Houston, a place known in American baseball circles as the 'Astros Pitcher Factory,' which has played a central role in the 'Player Development Revolution' over the past decade or so.

The man standing behind the bullpen mound before each game, watching the starting pitcher warm up, is current pitching coach Josh Miller, who has been deeply embedded in the Astros system for 15 years. He is a firsthand witness to the Astros' pitching development system, from nothing to something, from experimentation to maturity.

As one of the operators of the Astros Pitcher Factory, Miller never made it to the major leagues before retiring as a player. In 2009, he stepped onto the stage of Taiwanese professional baseball as a foreign player, playing for the La New Bears. He joined the Astros organization in 2011, working his way up from scout to minor league coach to major league pitching coach, personally experiencing the team's journey from rebuilding to a major transformation, leading the scientific revolution.

During the 2022 World Series, Miller appeared on an MLB Network program as the Astros pitching coach. When the host introduced him, he specifically mentioned Miller's journey from minor league player to scout, and how he had experienced the Astros' shift towards data, calling him 'on the front lines of the data revolution.'

Reflecting on his career, Miller said he developed a 'new way of watching baseball' by learning on the job in the Astros system. That way is to base all judgments on objective data, no longer relying solely on feel or just on what you see with your eyes. 'Anything that happens on the field, as long as it can be measured, has meaning.'

Miller told the Central News Agency that when Teng came to the Astros, he already had a fairly complete background in pitching analysis and was familiar with data, video, and the language of modern pitching training. What the Astros saw was a pitcher with a complete set of pitches, capable of starting or relieving, and willing to absorb information.

Miller said the direction of the Astros' collaboration with Teng was not to 'tear him down and rebuild him,' but to 'enhance his strengths.' His breaking ball was already a weapon; the team's job was to help him understand where to throw different pitches, how to combine them with his fastball, and how to attack the strike zone with more confidence during games.

When discussing pitcher development, Miller repeatedly returned to the concept of 'communication.' He does not pursue a top-down灌输 of ideas; he values how to help the pitcher digest and absorb information.

He said the team can provide objective data, video, and pitch tracking data, but ultimately, the player needs to buy in. 'We don't bang on the table and demand the pitcher do it,' but rather lay out the information, tell the player 'this is what we see,' and then listen to the player say 'what do you think, how do you feel, how have you done it in the past.'

'Over the past 10 years or so, baseball has become a job of managing an information system,' Miller said. With objective data, the main job of team management and coaches is 'how to get the player to buy in and agree with this approach. This requires sitting down and discussing, reaching a consensus, and knowing where we are going.'

Manager Joe Espada told the Central News Agency that he believes one of Teng's greatest traits is his 'open-mindedness and willingness to absorb information.' The Astros are very good at挖掘 the potential in players from other teams, acquiring them and then using a systematic training approach to amplify their strengths. 'Teng Kai-Wei is an example of that.'

Teng's signature 'sweeper' ranks among the top in terms of dominance for a single pitch type in the MLB. Two years ago, media reports, MLB official scouting reports, and even Teng himself called it a 'slider.' Miller, during the interview, also habitually called it a 'slider,' noting it was just a difference in the amount of horizontal movement.

What is the power of Teng's self-developed sweeper? Miller analyzed, 'Most pitchers, if they want to create this much horizontal movement, have to sacrifice velocity. But he can throw this pitch at 85 mph and still maintain the movement profile. It's truly unique. As long as he can throw it for a strike, hitters have to respect it.'

How is an elite-level breaking ball cultivated in modern MLB pitcher training? Miller said, 'It's the same for any pitcher; it requires constant trial and error, trying different grips, body feels, and mental cues.'

But Miller said this cannot rely solely on the pitcher's feel. The pitcher must throw in front of pitch tracking devices like TrackMan or Rapsodo, watch a lot of video, and be honest with their feelings and the results they produce in order to make fine adjustments and make the pitch sharper and harder to hit. (Editor: Wei Shu) 1150611

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