Which Hitters Changed their O-Swing% the Most in 2019?

A hitter doesn’t have to be selective in order to produce, but it certainly helps. Alex Bregman, Mike Trout, Mookie Betts, George Springer, Marcus Semien and Anthony Rendon were all among the top 10 percent of qualified hitters in terms of O-Swing% this season. In other words, they were among the choosiest hitters, swinging at pitches outside of the strike zone at exceedingly low rates.

Eddie Rosario, Tim Anderson, Javier Báez, Jeff McNeil, Nicholas Castellanos, Eduardo Escobar and Rafael Devers were in the bottom 10 percent for O-Swing%, proving that you can still be valuable in fantasy (and in real, actual baseball) without having even decent plate discipline. Some members of this group are simply good bad-ball hitters. Rosario, McNeil, Escobar and Devers were well above average at making contact with out-of-zone pitches. McNeil also made relatively high-quality contact on those offerings, posting an xwOBA (.314) that was 16 points above the average on out-of-zone pitches for hitters who saw at least 1,000 pitches this season.

In general, though, it’s better to be selective about the out-of-zone pitches one swings at. Common sense tells us that, but so does this graph. The hitters who stand the best chance of being productive on out-of-zone pitches — as measured by xwOBA — are the ones who swing at them at the lowest rate, and the hitters who have the worst chance are generally the ones who take the most whacks at balls out of the zone. The correlation this season, as reflected in an R-squared of 0.45, was strong. For the very best bad-ball hitters — Trout, Bregman, Rendon, Carlos Santana and Cody Bellinger, all of whom exceeded a .400 xwOBA on out-of-zone pitches — the combination of plate discpline and contact skills was essential. With the median xwOBA on out-of-zone pitches (.295, min. 1,000 pitches) being 49 points lower than the median xwOBA on in-zone pitches, making the most out of swings on out-of-zone pitches is important to a hitter’s overall production.

Given the importance of being selective, it’s helpful to see which hitters improved their plate discipline the most in 2019 and which saw the greatest deterioration in their plate discipline. As noted in the graph above, the trends for two hitters in particular caught my attention, and I will address them shortly. But first, let’s see which hitters reduced their O-Swing% by the largest margin in 2019.

Most Improved O-Swing%, 2018-19
Hitter 2017 2018 2019 2018-19 Change
Dansby Swanson 27.2% 36.5% 27.9% -8.6%
Mark Canha 37.7% 31.1% 25.0% -6.2%
Scott Kingery N/A 39.4% 33.7% -5.7%
Anthony Rendon 21.0% 28.9% 23.8% -5.1%
Dee Gordon 36.6% 41.4% 36.9% -4.6%
Jurickson Profar 24.3% 33.3% 29.0% -4.3%
Manuel Margot 29.0% 29.0% 25.0% -4.0%
Asdrúbal Cabrera 28.4% 32.3% 28.8% -3.5%
Marcus Semien 26.0% 26.2% 23.1% -3.1%
Nick Ahmed 36.8% 34.2% 31.0% -3.1%
Minimum 400 plate appearances in 2019

Dansby Swanson improved his plate discipline the most of any hitter who made at least 400 plate appearances this season, and he pulled away from the pack in that regard. His 2018 O-Swing% of 36.5 percent was an aberration, as he has had an O-Swing% below 29 percent in each of his other three seasons. This was not so much a new direction for Swanson as a confirmation of a trend from his first two seasons. The improved O-Swing rates for Mark Canha, Scott Kingery and Semien provide partial explanations for how each of these hitters made vast overall improvements in 2019.

Manuel Margot’s inclusion in this leaderboard is worth noting. While his improvement was not quite as great as that of Canha or Kingery, he took an unprecedented step forward like they did, rather than merely re-establish a prior level. Even so, his more selective approach did not do much to help his overall offensive production. Margot did record the highest HR/FB (9.8 percent) of his career, but that was largely neutralized by an uptick in strikeout rate (from 17.0 to 20.0 percent) and a minor dip in BABIP (from .281 to .272). His batting average fell from .245 to .234, and the needle barely moved on his OPS (.675 to .691) and wOBA (.288 to .296).

Margot’s apparent plateau could create an opportunity to get a potential breakout hitter in the endgame phase of 2020 drafts and auctions. Despite finding better pitches to hit and being an above-average contact hitter on out-of-zone pitches, his average exit velocity on flyballs and line drives actually decreased in 2019, falling from 92.8 mph to 91.1 mph. As Margot enters his age-25 season, it’s conceivable that he will rebound to hit with more thump next season, especially if his plate discipline doesn’t regress.

The biggest wild card for Margot is playing time. Andy Green went in phases with his outfield alignments, and he frequently benched Margot for several games in a row in favor of Wil Myers. The coming months will determine who out of Margot, Myers and Franchy Cordero will be center field options for the Padres come opening day. A trade to a less crowded outfield situation may be the best thing for Margot’s fantasy value. If he does find a path to regular playing time, he will not only have a chance to take advantage of his improved plate discipline, but also his increased stolen base efficiency (20 steals in 24 attempts in 2019).

The leaderboard for the players with the largest increases in O-Swing% includes only hitters who have recorded their highest rate in the last three years. Max Kepler and Bryce Harper are closest examples of hitters who regressed to a prior rate, and even they had higher O-Swing rates in 2019 than they did in 2017. The increase that could have the biggest impact on a player’s 2020 value is the one achieved by Yoán Moncada, as his O-Swing% ballooned from 23.3 percent to 32.7 percent. Even though his overall wOBA soared from .311 in 2018 to .379 in 2019, Moncada’s wOBA and xwOBA on out-of-zone pitches fell in each of the last two seasons. Both settled at a subpar .287 this season, and he was also below average at making contact with out-of-zone pitches. That’s a potential concern for Moncada, but in 2019, he compensated by being among the top 10 percent of hitters for both wOBA (.431) and xwOBA (.402) on pitches in the strike zone.

Most Worsened O-Swing%, 2018-19
Hitter 2017 2018 2019 2018-19 Change
Colin Moran N/A 29.2% 39.0% 9.8%
César Hernández 21.6% 20.3% 29.8% 9.5%
Yoán Moncada 26.8% 23.3% 32.7% 9.4%
José Iglesias 36.4% 39.7% 46.7% 7.0%
Enrique Hernández 27.0% 24.8% 31.7% 6.9%
Brian Anderson 30.9% 28.1% 34.8% 6.7%
Kolten Wong 25.2% 24.9% 31.4% 6.5%
Max Kepler 28.5% 24.9% 30.6% 5.7%
Bryce Harper 30.1% 26.1% 31.6% 5.5%
Kevin Pillar 40.1% 43.5% 48.8% 5.3%
Minimum 400 plate appearances in 2019

As I noted in my recent piece on Moncada and Kris Bryant, there are good reasons to be optimistic about the White Sox’s third baseman for the coming season, but early on, we should monitor his plate discipline. Any further erosion could make it difficult for him to approach his 2019 level of performance.

Al Melchior has been writing about Fantasy baseball and sim games since 2000, and his work has appeared at CBSSports.com, BaseballHQ, Ron Shandler's Baseball Forecaster and FanRagSports. He has also participated in Tout Wars' mixed auction league since 2013. You can follow Al on Twitter @almelchiorbb and find more of his work at almelchior.com.

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Will H.
Will H.

Canha, Iglesias and Pillar seem like the only ones with a multi-year trend. Have you looked back further to see if one-year changes are sticky?


Mark Canha’s 2017 is based off only 187 PA, so I’d guess that 38% is a bit of an outlier. His much fuller 2015 season he was at 34%. Just a reminder of small sample size demons that can live in data. Excellent article