Strikeout Rate Risers and Fallers for Week 10: Buy or Sell?

Due to a combination of harder throwers and hitters focusing on hitting for power, strikeouts are at an all-time high in baseball. For pitchers, this is an ideal trend. The ability to generate swings and misses is the most important skill to possess, as it's the only true way to control what happens after the pitch is thrown and eliminate the randomness that the ballpark, fielders, weather, and luck can play.

The stat is equally important for fantasy players. Not only are strikeouts a category in every league, but K-rates are often indicative of overall production. A pitcher with a 4.50 ERA with a 25.0 K% may see some positive regression in the future. On the other hand, a hurler with a 3.00 ERA and 16.0 K% may not see the ball continue to bounce their way.

In this column, we'll review two strikeout rate risers and fallers to determine if their performance will improve, hold steady, or worsen as the season moves along.

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Risers

Ross Stripling, Los Angeles Dodgers

2017 K-Rate: 24.3%; 2018 K-Rate: 30.1%; Last 30 Days: 35.3%

Ross Stripling has quickly moved from long reliever to a valuable rotation arm for the Dodgers. Injuries to Clayton Kershaw, Kenta Maeda, Rich Hill, and Hyun-Jin Ryu have made Stripling and Alex Wood the elder statesmen in the rotation, and the former has made the most of his opportunity. Through 48 1/3 innings, he owns a crisp 1.68 ERA, and his peripherals are almost equally impressive: 2.17 FIP, 2.74 xFIP, 2.79 SIERA. His strikeout rate is in elite territory, well above numbers he even posted against lesser competition in the minor leagues. The question is whether he can maintain this level of production.

From a strikeout perspective, the answer is doubtful. He's not getting a whiff rate expected from a truly elite strikeout artist, with a swinging-strike of 10.6%. That's barely above league average (10.4%) and below his 2017 rate (11.6%), in which he posted a 24.3% mark in the major leagues. That doesn't mean hope is lost, however. Stripling's curveball continues to get better, touting a 23.1% whiff rate since moving to a full-time starting role on May 6.

He has also increased the frequency with which he turns to the pitch, reaching a usage rate over 20% in his last two starts. Stripling's changeup has also played up while starting, boasting a 17.5 SwStr%. Both pitches are also elite groundball pitches, each getting hitters to roll over more than 70% of the time they're thrown.

Another encouraging sign for the right-hander is a lack of hard contact allowed coupled with his above-average groundball rate. Among all pitchers with 40 or more innings, only Justin Verlander has a lower hard-contact rate than Stripling (23.8%), and his average exit velocity allowed (84.4 mph) trails only Carlos Martinez and C.C. Sabathia amid starting pitchers with 75 or more hitters faced. He's also shown fantastic control with a 5.6 BB% and 70.9% first-pitch strike rate, over 10 percentage points better than the league average.

Stripling isn't going to maintain this kind of strikeout rate all season, but he's more than earned his spot in the Dodgers' starting rotation even when the other starters get healthy. Don't expect him to carry your fantasy pitching staff, but he'll remain a strong option moving forward.

Luis Castillo, Cincinnati Reds

2017 K-Rate: 27.3%; 2018 K-Rate: 22.5%; Last 30 Days: 26.4%

One of the trendy sleeper picks coming into the season, Luis Castillo is starting to round into his 2017 form. The second-year hurler got off to a brutal start, posting a 7.85 ERA and subpar 18.3 K% in his first six starts of the season. Over his last six outings, however, he's rounded into form with a 3.48 ERA and 26.4 K% in 33 2/3 IP. While he isn't quite the Castillo of his rookie year, there are encouraging signs abound.

First, the right-hander's SwStr% is even higher this year (14.7%) than it was in 2017 (12.6%). Only Max Scherzer, Chris Sale, Jacob deGrom, Noah Syndergaard, and Dylan Bundy are topping that number. Castillo's changeup is one of the most dominant pitches in baseball with a 50.8 O-Swing% and 29.8 SwStr% -- best among all starting pitchers. That's stayed consistent even when he was struggling. The improvement of his other pitches has led to the improved performance over his last six starts.

His pitch mix hasn't changed much, but his fastball command has been better and he hasn't missed out over the plate as much. While he's not getting as much velocity on his four-seamer this year, its whiff rate has risen from 7.7% in his first six starts to 10.6% in his last six. A change in arm angle has also led to a more effective slider, which has increased from an 8.2% to a 17.9% whiff rate.

The biggest red flag for Castillo is the amount of hard contact he's allowing. While he's improved in some regards, he's still leaving mistakes over the plate, as his Hard% has gotten worse over his last six starts. He's allowed six home runs in that time frame, and only 10 pitchers in baseball have allowed more long balls on the year. That number figures to stabilize, though, as his 19.7 home-run-to-flyball ratio doesn't figure to remain that high.

Although Castillo hasn't replicated his 2017 performance, his changeup alone makes him a potential elite source of strikeouts. Improved command is leading to better results, and further fine-tuning will continue to make him a quality buy-low option in the coming weeks.

Fallers

Lance McCullers Jr., Houston Astros

2017 K-Rate: 25.8%; 2018 K-Rate: 25.5%; Last 30 Days: 19.6%

Lance McCullers Jr. has drawn headlines for his wicked curveball, throwing it 24 consecutive times in last season's ALDS. But the pitch's lack of effectiveness in 2018 has played a heavy role in his strikeout rate trending in the wrong direction. In the last two years, McCullers became one of the first pitchers to start the trend of throwing a breaking ball as a primary offering, using it 48% and 49% of the time in 2016 and 2017, respectively. In his first four starts of 2018, that trend continued as he used the breaking ball 52% of the time. The results were promising, as he fanned 34 batters in 21 innings.

Since that time, however, his strikeout rate has taken a dive. He has 35 strikeouts in his last 42 1/3 innings pitched, though he's still pitching well overall with a 3.40 ERA in those seven starts. The curveball, which had a SwStr% in excess of 18% in each of the last two seasons, has fallen to 15.1% in 2018. Across his last seven outings, its whiff percentage is a mere 12.8%, down from 20.1% in his first four starts. The pitch is currently being hit for a .390 slugging percentage, a career-worst mark for McCullers. According to the pitcher himself, he just hasn't had the same feel for it this year, which shows up in the declining vertical movement numbers.

Hope isn't lost for McCullers' strikeout potential, though. While his curveball hasn't performed the same for the right-hander, his changeup has become a plus pitch. Its his weapon of choice 16.7% of the time, well up from his previous season-high of 10.9% set last year. As he's decreased his curveball usage to 38.8% in his last seven starts, his changeup has increased to 20.6% from 8.7% in his first four outings of the year. The offering has only gotten better with increased focus, touting a career-best 21.5 SwStr% that's significantly higher than his previous high of 12.9% in 2017.

Paired with a sinker that gets groundballs over 60% of the time it's put into play, and McCullers has a solid three-pitch mix to work with. He's still getting batters to chase outside the strike zone (31.4 O-Swing%) the way he has for most of his big-league career, and his overall SwStr% (12.4%) is solid. If he can regain the feel for his curveball, he's going to have two dominant putaway pitches he can turn to with two strikes, and that will make him a pitcher any fantasy manager is lucky to have. In the meantime, he's still a player most players would be glad to own, but he's not quite ready to be the strikeout artist he was in the first four games of 2018.

Sean Manaea, Oakland Athletics

2017 K-Rate: 20.2%; 2018 K-Rate: 18.4%; Last 30 Days: 12.8%

A trendy waiver-wire add after his huge April, including the season's first no-hitter, Sean Manaea has been rather mediocre since then. Manaea owned a 1.42 ERA and 23.8 K% in the first month of the year, but he's allowed four or more earned runs in five of his six May starts and has returned to being a fairly pedestrian strikeout pitcher. The southpaw tied a career-high with 10 punch-outs in his no-no on April 21, but has only 26 in his last 38 1/3 innings. To this point in his career, Manaea hasn't been able to translate his high strikeout rate in the minor leagues (28.3%) to the majors (20.1%), which has limited his overall fantasy value.

When he found success in April, both of Manaea's secondary pitches were working well. His slider had an 18.8% whiff rate and a minuscule .087 slugging percentage allowed, and his changeup was right behind at 17.8% and .233. That gave him a nice combo to go with his fastball, which he was commanding well. There were signs of regression; namely, his unsustainable .148 batting average on balls in play allowed and 98.2% strand rate. But the way he was missing bats showed he still had the potential for a breakout.

Since the calendar flipped to May, both putaway pitches have gone down the tubes. His changeup fell to a 13.3% whiff rate and .500 slugging percentage for the month, while his slider dropped to an abysmal 8.2% and was crushed for a .643 SLG. As a result, he's stopped using his slider as much, throwing it only 11.6% of the time in May while relying more on the change.

That's hurt his effectiveness with both pitches. His slider isn't getting batters to chase like it has in the past, currently sitting at a career-low 34.7% O-Swing rate for the season. The contact rate for both pitches has, unsurprisingly, risen as well, with his slider sitting at 67.1% and his change at 70.5%. His previous career-worst marks were 60.6% and 65.9%, respectively.

The underlying numbers don't provide a ton of reason for optimism for Manaea, as he's giving up a ton of hard contact right now in addition to his swing-and-miss numbers dropping from last year. His soft-contact rate fell tremendously from a solid 19.6% in April to 8.6% in May as his average exit velocity increased from 88.3 to 90.3 mph. The lefty is out of whack right now, and until he finds more consistency and unlocks the strikeout potential he showed in the minors, he's not an arm you can trust to start on your fantasy team.

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