Strikeout Rate Risers and Fallers for Week 8: 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

Chad Kuhl, Pittsburgh Pirates

2017 K-Rate: 20.9%; 2018 K-Rate: 22.2%; Last 30 Days: 26.3%

Although more starting pitchers can approach triple on the radar gun than ever before, the group is still relatively small. Chad Kuhl is one man who can do it, regularly hitting the upper 90s on the radar gun with his sinker. The pitch averages 95 mph, a number topped only by Noah Syndergaard this season. Despite that, however, Kuhl has never been a huge strikeout pitcher. With a new curveball in his arsenal, he took a step in the right direction in 2017 and posted his highest strikeout rate as a professional. Kuhl has made further progress in 2018.

Over the last 30 days, Kuhl is in the top-25 among starting pitchers in strikeout rate, fanning 30 batters in 28 innings. Overall, the right-hander's swinging-strike rate is actually down from last season (9.3% vs. 9.5%) despite the higher strikeout rate. In his five starts over the last month, however, the uptick in swinging strikes isn't just coming from painting the corners. He's getting a few more swings and misses (10.7% whiff rate, right at the league average), a much more sustainable way to maintain strikeouts.

A sharper slider has been Kuhl's most effective weapon for missing bats, as the pitch's whiff rate has risen from 16.1% in his first four starts to 21.8% in his last five. His curveball has become an above-average pitch as well, despite the fairly mediocre whiff numbers (10.7%). Adding a four-seam fastball to his repertoire has also made his sinker slightly more effective, particularly against left-handed hitters, as it's sitting at a career-best 7.0 SwStr%.

Still, his SwStr% doesn't indicate a pitcher who's likely to maintain a 26% strikeout rate the rest of the season. There's another red flag to be aware of, too: Kuhl isn't getting many batters to chase outside the strike zone. His O-Swing% (23.4%) is well below league average (29.9%), even over his last five outings (25.6%). This is an important skill for pitchers to have because it means their stuff is fooling hitters into swinging at bad pitches. The 2018 leaderboard, unsurprisingly, consists of some of the top pitchers in the game: Chris Sale, Syndergaard, Justin Verlander, Jacob deGrom and Max Scherzer are all in the top 15. A low number isn't the end of the world, as guys with particularly nasty stuff — like Carlos Martinez or Jon Gray — can still maintain a high K% with a below-average O-Swing%. But, velocity aside, Kuhl doesn't really fit into that category.

So, this isn't quite the breakout some were hoping for Kuhl given his elite velocity, but he's shown some progress by adding new pitches as well as reducing his walk rate from 10.6% last season to 8.5%. Although he has some work to do regarding consistency — particularly when it comes to command and keeping the ball in the park (1.63 HR/9) — Kuhl is a decent source of strikeouts in deeper leagues. Until he shores up other aspects of his game, though, his ownership should likely stay exclusive to NL-only or 12- and 14-man leagues.

Michael Fulmer, Detroit Tigers

2017 K-Rate: 16.9%; 2018 K-Rate: 21.1%; Last 30 Days: 25.2%

Michael Fulmer is cut from a similar cloth as Kuhl. He throws really, really hard, but his strikeout numbers leave something to be desired. Through his first two major-league seasons, he struck out only 18.6% of the hitters he faced, a number you wouldn't expect from a pitcher averaging 95 mph on his fastball and touching 99 at times. Last year, an elbow injury almost certainly affected that number, which fell to 16.9% after sitting at a slightly below average 20.1% in his rookie season in 2016. It looked like that trend was continuing early in 2018. His K% fell even further to 13.0% through his first four outings, a significant concern for the once-top prospect. The light seemingly came back on over his last five starts, however, in which he boasts a 28.0 K%.

What changed? Fulmer has gone away from using his sinker so much and introduced the four-seamer into his pitch mix more frequently. Through his first four starts, he used the sinker on 41.6% of his pitches and the four-seamer just 12.6% of the time. Over his last five outings, the sinker usage has fallen to 30.3% and the four-seamer has risen to 27.8%. His sinker has been bashed around like never before in 2018 (.377 wOBA), so Fulmer has adjusted by throwing something straighter and going up in the zone with more regularity. Fulmer's four-seamer currently has a 15.1 SwStr%, which is almost unheard of for a fastball. Take a look at where he's getting most of his swings and misses over his last five starts compared to the first four:

Fulmer has also revamped his slider and is seeing fantastic results. The pitch is getting significantly more horizontal movement than in years past — nearly four more inches than last season — and the whiffs have gone up as a result. His slider has a 17.6 SwStr%, well above his previous career-best of 14.1% set last year.

By most metrics, this looks like a sustainable change for Fulmer. His overall SwStr% has gone from 9.3% in 2017 to 11.4% this year, well above league average. He's also among the league leaders at getting hitters to chase outside the strike zone (36.0%), with his slider and four-seamer seeing sizable increases. Fulmer's last three starts haven't been great (14 earned runs in 16 1/3 innings), but with these encouraging changes, he's someone to target via trade while his value is still relatively low.

Fallers

Jose Berrios, Minnesota Twins

2017 K-Rate: 22.6%; 2018 K-Rate: 23.5%; Last 30 Days: 18.4%

One bad start aside, Jose Berrios took baseball by storm to begin the 2018 season, allowing no runs in three of his first four outings while striking out 29 in 27 2/3 innings. At no point was his talent on better display than in his seven shutout innings in a game in his homeland, Puerto Rico, on April 18. But after that game, everything started to go sideways for the 23-year-old. Over his next four starts, he allowed 18 runs in 18 1/3 innings. In the first of those appearances, he struck out seven. In the next three, he fanned only four batters.

When Berrios is on his game, his curveball gets tremendous horizontal movement and piles up whiffs. Through five starts, he got whiffs on the pitch 22.2% of the time he let it loose. Its effectiveness suddenly disappeared over three outings from April 29 through May 10, getting swing-and-miss rate of just 5.8%. The difference was pretty simple: he stopped getting as much horizontal movement on the pitch, and hitters were better able to connect with it. Take a look at the drop from his first four outings against his most recent four (Note: The game in Puerto Rico is not counted since the PITCHf/x and Statcast systems are not set up at Hiram Bithorn Stadium.):

The drop doesn't seem like much at first glance, but a difference of even as little as an inch makes a huge difference. Berrios' curveball movement hit a season low on May 10 against the Angels, getting just 7.83 inches of horizontal ride and zero whiffs. Berrios needed a bounce-back outing in the worst way on Tuesday against the Cardinals and got it. As the chart illustrates, he had his best curveball movement since his start against the Yankees on April 24. Although it wasn't quite getting 10+ inches of movement, a rebound back to 9.23 inches helped significantly. He got nine whiffs on the curveball and had his best outing in nearly a month, striking out 10 in 7 1/3 innings and allowing one run on two hits.

As long as his curveball is working, there's a lot to like with Berrios and he'll continue to be a fantasy asset. His other pitches are only getting better, too. His changeup currently has a 15.2 SwStr%, up from 7.3% in 2017, though he's only using it about 9% of the time. Perhaps his biggest improvement has been with the sinker, which is getting hitters to chase a whopping 40.0% it's thrown outside the strike zone, a huge increase from the 28.3 O-Swing% it had last year. As a result, Berrios' groundball rate on the sinker has risen from 47.3% to 56.5%. He'll have ups and downs like any young pitcher, but his last start should ease the mind of fantasy players who were looking to sell.

Danny Duffy, Kansas City Royals

2017 K-Rate: 21.4%; 2018 K-Rate: 18.7%; Last 30 Days: 14.6%

Despite his solid 3.81 ERA in 2017, many fantasy players were skeptical of Danny Duffy coming into 2018. After posting a career-high 25.7 K% in 2016, the number became merely average (21.4%) last year. Which Duffy would show up in 2018 was a mystery, especially after he lost nearly two miles per hour on his fastball between '16 and '17. The southpaw's velocity hasn't returned to its former mid-90s average. Neither have the strikeouts, despite promising returns early in the year. Accordingly, his ERA has skyrocketed to 6.88 ERA, and peripherals don't paint a prettier picture, either (6.48 FIP, 5.39 xFIP).

Even though Duffy's K% was down in 2017, he still had an above-average 11.4 SwStr%, which was a primary reason for hope of a return to his 2016 form this year. That number has taken a huge hit instead, dropping to 9.4% through 51 innings. After boasting a 25.6 K% through four starts, back in line with his 2016 breakout, the number has dropped to 14.6% over his last six. The main culprits are his changeup and slider, which have both dropped off considerably in quality. In his first four starts, Duffy got 19 total whiffs on his change; that number has fallen to five over his last six starts. The slider hasn't fallen quite as hard, but it's gone from a 16.4% whiff rate to 13.4%.

It's clear that neither pitch is fooling hitters, as the O-Swing% on both has tanked in 2018:

Command has been Duffy's primary problem. In addition to boasting his worst strikeout rate since 2015, Duffy's walk rate has spiked to 10.4%. He's throwing the ball in the strike zone on only 43.9% of his pitches versus 50.7% in 2017 and 49.8% in 2016, with significant dips on all his offerings except the slider. With the decreased velocity and control problems, he's not someone worth holding onto in most fantasy leagues at this point.

More 2018 MLB Advice and Analysis