Strikeout Rate Risers and Fallers for Week 15: Buy or Sell?

Strikeout rate risers and fallers based on RotoBaller's premium tool. Matt Wilkes identifies some starting pitchers (SP) whose changes in K rate could make them worth adding or dropping in fantasy baseball leagues.

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

Danny Duffy, Kansas City Royals

2018 K-Rate: 19.2%; Last 30 Days: 24.2%

After an appearance on the Fallers portion of this column earlier in the season, Danny Duffy reappears, this time on the positive half of the article. Let's face it: the Royals' ace still has horrific numbers overall. In 100 2/3 innings, he has a 5.19 ERA (5.39 FIP, 5.23 xFIP), a career-worst 33.0 groundball rate, 19 home runs allowed (1.7 HR per nine innings, another career-worst number), a 10.7% walk rate, and his lowest strikeout rate since 2015. Over his last five starts, however, Duffy has shown signs of righting the ship. Although he's largely been hit and miss in those 31 innings, allowing either six-plus runs or one run or fewer in each outing, it's resulted in a 3.77 ERA and 24.2 K%.

Whether that's sustainable is up for debate. On one hand, his stuff is crisper. He's raised his swinging-strike rate to 10.0% on the season with a 12.6 SwStr% over his last five starts, and his velocity has increased to an average of 94 mph since sitting at 93 in April. On the other hand, he's still not getting batters to chase outside the strike zone like we're accustomed to seeing. For his career, his O-Swing% sits at 29.1%, which isn't too far off his 28.7% rate for the season. But that number is well below his rates from the last two seasons (well above 30% both years) and the league average (30.5%). Over his last five starts, that number is even worse (27.6%) despite the increase in strikeouts and whiffs.

A large reason for that is he's gone away from his slider, which along with the changeup had been his best swing-and-miss pitch in 2016 and '17. It simply hasn't been effective this year (-9.5 pitch value), and he's made the curveball his breaking ball of choice during his hot stretch.

The curve, however, boasts a mediocre 9.3 SwStr% on the season, which is in line with his last five starts as well. Along with giving hitters two breaking balls to contend with, using the slider less has perhaps made it more effective, seeing it's whiff percentage rise to 17.0% in his last five starts.

The biggest source of his swings and misses, though, has been his fastball. Since June 9, only Chris Sale and Justin Verlander have a higher percentage of whiffs on the pitch than Duffy (16.9%) among starters who've thrown the pitch 150 or more times, according to Statcast data. However, Duffy doesn't have the above-average spin rate of Sale, Verlander, and other pitchers who get a high number of whiffs on their fastballs, so it remains to be seen if this increase lasts. His career numbers on the four-seamer (8.3 SwStr%) suggest the answer is probably not.

At the end of the day, more data is needed before it can be determined whether Duffy has become a reliable source of strikeouts again (or a reliable fantasy arm in general). Even with the uptick, his results have been largely inconsistent and the walk rate remains problematic, making him hard for fantasy owners to trust.

Mike Clevinger, Cleveland Indians

2018 K-Rate: 22.2%; Last 30 Days: 26.1%

Mike Clevinger's second season as a permanent member of the Indians' rotation has been arguably even more impressive than his 2017 campaign. His walks are way down (8.1 BB% vs. 12.0% in 2017), his groundball rate is up (43.0%), his ERA is exactly the same (3.11 ERA), and he's already amassed more fWAR (2.7) in 11 fewer innings than last year, when he was worth 2.2 fWAR on the season. But one component has been missing: strikeouts. The right-hander fanned 27.3% of hitters he faced last season; this year, that number is down to 22.2%. Over the last month, that trend has reversed, to the delight of fantasy players everywhere.

The weirdest part? His O-Swing% and SwStr% are nearly identical over his last five starts (31.0%, 11.5%, respectively) to his totals in his first 12 (31.1%, 11.2%). Does that mean his strikeout numbers are a fluke? Possibly. But more than likely, his numbers are starting to come up to expectations. Both his O-Swing% and SwStr% are above average, yet he boasted a strangely low strikeout rate (20.5%) in his first 12 starts and still sits below the league average for the year. Among 28 qualified pitchers with an 11.0 SwStr% or better, Kevin Gausman and Alex Wood are the only others with a below-average strikeout rate.

While Clevinger's strikeouts seem to be normalizing, he's still not missing bats at the same rate as he did in 2017 (12.4 SwStr%), though his chase rate is up considerably. Throwing more strikes may be playing a role in that. In 2017, he could reasonably be classified as "effectively wild." But now that he's pounding the strike zone with more regularity, hitters are swinging more. Batters are offering at 46.6% of Clevinger's pitches as opposed to 42.2% last season, and they're making more contact (75.8% vs. 70.5%). Those numbers have largely held the same even during his strikeout increase (45.7% Swing%, 74.8 Contact%).

But he has made some changes that have helped him get more strikeouts. Most notably, he's added some extra spin to his fastball. In his first 12 starts, his four-seamer averaged 2,268 revolutions per minute. That's jumped to 2,334 over his last five outings, putting him above the league average for the pitch (2,289). It's made a difference, taking his fastball from a pedestrian 6.7% whiff percentage to 12.1%. His curveball, while not getting any extra spin, has also increased from a 16.1% to 20.4% swing-and-miss rate. However, his slider has suffered dramatically, falling from 20.9% to 10.7%, and his changeup (13.5%) — while holding steady — remains well below last year's rate (18.5%).

Based on the numbers, Clevinger doesn't seem poised to start striking out hitters the way he did last season, but his numbers are starting to normalize based on his SwStr% and O-Contract%. With an impressive four-pitch mix paired with better control, he should continue to be a valuable fantasy arm, even if his 6.2% HR/FB doesn't hold up.

Fallers

J.A. Happ, Toronto Blue Jays

2018 K-Rate: 26.3%; Last 30 Days: 19.0%

At 35, J.A. Happ suddenly became a strikeout artist in 2018, continuing a late-career breakout at an age where most players are expected to decline. The southpaw, though he holds an unflattering 4.44 ERA, has a strikeout rate that ranks 19th among all qualified pitchers — better than the likes of Carlos Carrasco, Corey Kluber, Aaron Nola, and Zack Greinke. You read that correctly. A veteran with a career 20.6 K% who never had better than a 23.0 K% in a season (back in 2012) is a premier strikeout pitcher in 2018. Although there were some compelling reasons for that increase, it seemed unlikely to last all season based on his career averages. And that regression has seemingly started.

After fanning an eye-popping 87 hitters in his first 70 2/3 innings, Happ has only 28 strikeouts in his last 34 2/3 frames. His SwStr% has dropped from 11.2% to 7.7%. Given that the southpaw never posted a rate better than 9.6%, that number figured to normalize over time, and that process has started. His Contact% has also spiked from 75.2% to 84.4% in his last six outings, though he still has a healthy 31.9 O-Swing% in that span.

When he owned a strikeout rate above 30% early in the season, the southpaw was bucking the usual trend and using his fastball to get most of his swings and misses, with the majority coming on pitches up in the zone. While the spin rate on his four-seamer remains above average and his velocity hasn't changed, hitters aren't missing those pitches up in the zone as much. Here's a look at his whiffs per swing in his first 12 starts versus the last six:

While all of this probably means Happ isn't going to keep striking out hitters the way he did early in the year, he's not a useless fantasy pitcher by any means. Only 10 pitchers have allowed a lower hard-contact rate than Happ this season (29.6%), and his Soft% (20.1%) ranks in the top 30 as well. He won't kill you with walks either, boasting a respectable 7.8 BB% that falls right in line with his marks from the last three years. But if you can get a fellow player in your league to overpay for the strikeout total, now is the time to pull the trigger while selling (somewhat) high is still an option.

Tyson Ross, San Diego Padres

2018 K-Rate: 21.1%; Last 30 Days: 15.1%

Another recurring name in this column is Ross — only this time, he's on the wrong side of the list. After an out-of-nowhere resurgence to begin the year, the right-hander has fallen on hard times lately. He's been pounded for 15 runs in seven innings over his last two starts and, more concerningly, his strikeout have evaporated. The 31-year-old has only 21 in his last 31 1/3 innings pitched to go with a 6.89 ERA, making him impossible for fantasy players to trust and likely lowering his trade value for the Padres. Ross is undoubtedly in droppable territory in most leagues. Is there any hope for a turnaround, or is it time to cut bait on what was an early-season feel-good story?

The drop in strikeouts isn't terribly surprising when glancing at the numbers in his first 12 starts, as his 9.9 SwStr% didn't support an above-average K%. Here's what we noted the first time Ross was mentioned in this column nearly two months ago when he was holding a 27.0 K%:

"Ross likely won't maintain a strikeout rate this high all season long unless he gets more whiffs. His 10.3 SwStr% is below league average (10.6%) and his career rate (10.7%)."

That has proven true, as his SwStr% continues to plummet along with the strikeout numbers. In his last six starts, Ross has a paltry 7.7 SwSt% — only 10 pitchers have a worse rate in that time frame. Ross' O-Swing% has also fallen from 32.4% to 28.5%. Naturally, batters are hitting the ball harder against the right-hander, whose Soft% has dropped from an impressive 21.4% to a poor 15.8%.

Ross is one of the many pitchers who's throwing his best pitch, the slider, most often. He's still using it at a similar rate (41.0%) but is getting fewer whiffs (14.4% vs. 15.7%). The main reason seems to be the pitch is getting less bite (i.e., vertical movement).

Even a fraction of an inch can make a difference between swinging through a pitch and making contact, and that's been apparent in Ross' results. But there's another factor potentially at play: his pitch mix. In his first 12 starts, Ross used the four-seamer as his primary fastball, mixing in a cutter about 13% of the time. That proved a successful approach, as his cutter registered a whiff percentage of 12%, giving him two decent pitches to go to when he needed a whiff. He's used the cutter more over the last month (about 20% of the time) and reduced his four-seam usage from 36% to 28%. He may have overdone it a bit, though, as the cutter has ceased to be a swing-and-miss pitch with more use (5.7 whiff%).

Going back to his April and May pitch mix may be in Ross' best interest, though he was unlikely to stay on the same strikeout pace from those two months anyway. Combining the strikeout decrease with a lot of hard contact, the results haven't been pretty since June began. Ross has a .373 xwOBA in that time, a number topped by only 11 other starters who have faced 100 or more batters in that time. Despite a promising beginning to the year, the right-hander is on the way back to fantasy irrelevance.

All stats as of Sunday, July 8.

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