For the last four seasons, MLB has seen an increase in strikeout rate (K%). Since 2015, K% has increased from 20.4% to 23.0%. We’ve also seen an increase in walk rates and a poorer league-wide ERA. Those trends can make it difficult to assess whether a pitcher is actually better at inducing swings and misses.

Despite that potential difficulty, K% is critical in evaluating a pitcher’s future success: as one half of K-BB%, and a significant component in a number of ERA predictors, strikeouts help explain changes in a player’s performance and indicate future performance.

Without further ado, here are 2019’s biggest K% risers:

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Top Strikeout Risers (SP)

Lucas Giolito, Chicago White Sox

2018 K-Rate: 16.1%; 2019 K-Rate: 32.3%

It’s no surprise to see Giolito’s name at the top of this list. He was a late-round buy in most leagues, and his ascent to ace-status was directly paralleled by his K%. The increase in his K% was unrivaled this season, and it helped him to finish the season as SP13 in standard formats. His 32.3% strikeout rate was the fourth-highest among qualified starters with 228 total strikeouts. The improvement came from a combination of improved control and velocity, which forced batters to chase more frequently and induced more swinging strikes.

Frankie Montas, Oakland Athletics

2018 K-Rate: 15.2%; 2019 K-Rate: 26.1%

It’s hard to say exactly how much of Montas’ growth was tied to the PEDs, but we do know that he added a splitter, and he was just 25 years old entering last season. Montas has always thrown heat, so we should not dismiss his progress. In 2019, he threw fewer pitches in the zone than he has at any point in his career, and he did that while maintaining a 60.7% first-pitch strike rate and achieving the best O-Swing% (32.7%) and Swing% (49.1%) of his career. It’s possible that the PEDs allowed Montas to throw harder with less effort and thus improved his control, but it certainly seems like we’re talking about more development than that.

Mike Clevinger, Cleveland Indians

2018 K-Rate: 25.6%; 2019 K-Rate: 33.9%

On a certain level, this was the season that Mike Clevinger was supposed to have. By that, I mean that pre-season expectations were already sky-high for Clevinger proponents. After all, he finished 2018 with a 3.02 ERA and 169 Ks in 200 IP. In 2019, however, Clevinger’s strikeout rate shot up, and his 33.9% sits right between Max Scherzer’s 35.1% and Giolito’s 32.3%. Of course, Clevinger only threw 126 IP due to injuries, but on a certain level, that makes his strikeout rate even more impressive. The Cleveland righthander increased his fastball velocity to 95.5 MPH and his swinging-strike rate from 12.0% to 15.2%. Those changes combined with a lower BB%, and they forced batters into pitcher-friendly counts far more often than 2018.

Elieser Hernandez, Miami Marlins

2018 K-Rate: 15.9%; 2019 K-Rate: 24.1%

Inconsistency defined Hernandez’s 2019 season. He did pitch six games in relief, but in a surprise, he struck out batters more frequently when he was starting, so he’s on this list for having bumped his strikeout rate by 8.2%. Despite not being a high-velocity or high-whiff pitcher, Hernandez’s strikeout rate of 24.1% is much closer to the 25% he managed in the minors. Unfortunately, Hernandez struggled in the second half of the season, and those struggles directly correlated to his inability to earn strikeouts after the All-Star break. Notably, Hernandez’s O-Swing% seemed to fluctuate in similar patterns to his strikeouts and overall success. That pattern was definitely tied to his pitch use. The more Hernandez relied on his fastball, the more he tended to struggle. When he used his changeup and slider more frequently, he improved his O-Swing% and saw greater success. If he can rely less on his fastball, he’s a candidate to take a step forward in 2020.

Sonny Gray, Cincinnati Reds

2018 K-Rate: 21.1%; 2019 K-Rate: 29.0%

As MLB’s league-wide K% increased over the last three years, Gray’s personal rate stagnated during his time with the Yankees. Gray asserts that New York asked him to change his approach and to use his slider in more situations than he wanted. After arriving in Cincinnati, Gray used his curve more frequently and threw fewer fastballs. However, he actually threw more sliders than he did in either season with the Yankees. Interestingly, even though the Reds did less to push the pitch, Gray used it to generate 68% more swinging strikes than in 2018. If Gray is to be believed, the change was simply about how and when he was using the slider. If that change is lasting, Gray may well be a poor man’s Patrick Corbin.

Matthew Boyd, Detroit Tigers

2018 K-Rate: 22.4%; 2019 K-Rate: 30.2%

Boyd’s hot run at the start of the season garnered plenty of attention. The Detroit righty started throwing his best pitch, his slider, more and more. From March through July, Boyd used his slider 37.1% of the time. That peaked in July when he was throwing it at a rate of 41%. Unfortunately, he struggled in the second half, and there was a definite correlation to how much he was using his curve and slider during those months. In late July and early August, Boyd was throwing his slider almost as much as his fastball, and it appears that hitters responded by starting to wait for the slider. During his August and September, the ISO against Boyd’s slider spiked to .220 and .350 respectively. His K% dropped to 25.0 during those months, and his ERA jumped accordingly. It’s not clear where that leaves him. Certainly, the ability is there, and Boyd showed he’s capable of adjusting to how hitters approach him, but he may not be able to recapture the same level of strikeout success in 2020.

Luke Weaver, Arizona Diamondbacks

2018 K-Rate: 19.9%; 2019 K-Rate: 26.5%

Coming into 2019, we all knew what Luke Weaver was: a guy with two strong pitches and limited strikeout ability once the league had scouted him. During the 2018-2019 offseason, Weaver retooled his curveball and decided to bring back the cutter he used in 2016. The change allowed Weaver to be far more dynamic. Despite throwing his fastball and changeup less frequently, the pitches generated higher pVal scores (a volume-based metric). Weaver advanced in nearly every facet of batter-hitter contests: he set career bests in O-Swing% (30.2), Z-Swing (46.4), and SwStr% (10.4). Weaver’s final K total of 69 in 64.1 IP was modest because he spent most of the year recovering from a forearm strain and UCL strain, but 2019 gave plenty of reasons for optimism about the 26-year-old.

Homer Bailey, Free Agent

2018 K-Rate: 15.2%; 2019 K-Rate: 21.4%

The change in Bailey’s K% isn’t a revelation or personal overhaul as much as a return to health. The last time Homer Bailey had more than 30 starts in a season was 2013, when he was 27 and managed a K% of 23.4%. Bailey has lost two MPH since then, and his splitter has become his best pitch, but he looks like the same pitcher he was for the last two seasons, just with better health. If he’s healthy to start 2020, he’s worth a late-round flyer for next season. Managers shouldn’t rely on more than 100 IP from him. Steamer projects Bailey at 142 IP, but he’s averaged only 90.3 IP since 2014.

Shane Bieber, Cleveland Indians

2018 K-Rate: 24.3%; 2019 K-Rate: 30.2%

Which superlatives best describe Bieber’s season? Extraordinary? Exceptional? Electric? The Cleveland right-hander started his sophomore season as a promising arm who projected as a top-25 starter, and he now seems like a contender for next year’s Cy Young. Bieber’s K% surged to 30.2%, which was good enough for 10th among qualified leaders. In 2019, he threw all of his breaking pitches harder than the year before. Bieber also seems to have made it harder to distinguish between his slider and curve; the pair confounded hitters, and Bieber used the combination to achieve a 35% O-Swing% and a 14.0% SwSt%. Managers should see him as one of the more reliable arms in the early draft.

Luis Castillo, Cincinnati Reds

2018 K-Rate: 23.3%; 2019 K-Rate: 28.9%

Castillo might be the most interesting story of all the names here. In 2019, he dropped his fastball use to a mere 30% and increased his changeup to 32%. He was able to get away with that change because he still throws his sinker at 96 MPH and because he added movement to his changeup. The result was improvement across the board. Batters chased more pitches outside the zone, they watched more pitches inside the zone, and they swung and missed at a rate of 15.9% (4th best among qualified starters). Castillo’s inconsistency may scare off some owners, but the strikeout ability is real.

Honorable Mentions

Gerrit Cole, Free Agent

2018 K-Rate: 34.5%; 2019 K-Rate: 39.9%

The league’s best pitcher right now, striking out fools at a nearly 40% clip. Elite reliever K%, but seven innings at a time. Unreal.

Martin Perez, Free Agent

2018 K-Rate: 13.1%; 2019 K-Rate: 18.3%

Through June, he was averaging a 21.3 K% and a 3.74 FIP. Somehow only 28 years old and showing the best plate discipline numbers of his career. He’s worth a flier in deep leagues.

Lance Lynn, Texas Rangers

2018 K-Rate: 23.0%; 2019 K-Rate: 28.1%

At the age of 32, he increased his velocity for the second year in a row and set a career-high in strikeouts. I keep thinking about Charlie Morton.

Andrew Heaney, Los Angeles Angels

2018 K-Rate: 24.0%; 2019 K-Rate: 28.9%

Velocity seems back to 2016 levels, but he managed only 95.1 IP this year.