Using K-BB% To Find Relievers to Add for the Second Half

Eric Samulski identifies relief pitchers (RP) worth adding on the waiver wire in fantasy baseball for the second half of the 2021 MLB season based on K-BB%.

A couple of weeks ago, I used June's K-BB% leaderboard to look at which starting pitchers might provide value in the second half. In that article, I explained why I loved the metric so much by stating:

If a pitcher has a high strikeout rate (K%), then we know he is effective because we know that strikeouts and good and a sign of deception and good stuff. However, if a pitcher also has a high walk rate (BB%), then we know that the pitcher can't harness that stuff and gives up a lot of baserunners. K-BB% thus allows us to identify pitchers who can not only miss bats but also have the command to make use of their strong pitches.

The metric is most impactful when looking at relievers. Since relievers strikeout batters at a higher rate than starters, we expect to (and want to) see high strikeout totals. This is also essential since the best relievers are used in high-leverage situations where strikeouts are crucial. However, even relievers with the best stuff can be undone by inflated walk rates (see Jose's Alvarado's 18.6% rate or Aroldis Chapman's 20.4% rate in June). Since the top-five relievers this season based on K-BB% are Liam Hendricks, Craig Kimbrel, Matt Barnes, Josh Hader, and Raisel Iglesias, I think we might be onto something.

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K-BB% Leaders at RP

I decided to create a K-BB% reliever leaderboard from June 1st to the All-Star Break with the hope of seeing if any names jump off the page that might be on most waiver wires. Since we know there will be a lot of bullpen turnover around the trade deadline, this could give us an early jump on stashing some guys that become high-impact arms. The full leaderboard is posted here and then I'll dive into some specific names below.

Tyler Wells - RP Baltimore Orioles

I'm not going to lie, I didn't expect to see Wells so high; however, the Rule 5 pick was particularly impressive in this last series against Boston, and I'm sure Minnesota wouldn't mind having him on the big-league roster with Alex Colome and Hansel Robles scuffling. Wells is a behemoth at 6'8" 255 pounds, pumping 95 mph on the fastball and pairing that with a changeup and slider that both have under .200 xBA.

Despite using the slider more, the changeup has actually been his best pitch with a 25.4% swinging-strike rate (SwStr) and 33.8% CSW; although, we shouldn't sneeze at the 18.8%  SwStr% or 28.2% CSW on the slider. In fact, even the four-seam has a 15.5% SwStr, which gives Wells three swing-and-miss pitches. Since he throws the slider mostly to righties and the changeup mainly to lefties, he hasn't yet produced any meaningful splits and should be impactful regardless of who he faces. Baltimore has a bit of a feisty lineup that will produce runs in the hot summer months, so don't be surprised if Wells vaults to the top of this closer group in a few weeks.

Paul Sewald - RP Seattle Mariners

Sewald is the cover boy, and I'm sure not many people had any idea who it was when they first saw the image. Sewald is a 31-year-old whose best season was posting a 4.55 ERA in 65.1 innings out of the bullpen for the Mets in 2017. However, this is not the same guy, and the biggest reason for that might be the jump in spin rate on his fastball. For much of his career, Sewald threw 91 mph with a fastball spin rate around 2250 and over 20 inches of drop. Since we don't want drop on four-seam fastballs but rise, that's not ideal.

However, in 2021, Sewald is throwing 92.5 mph with a 2430 spin rate and 18.5 inches of drop, which is now above average versus other similar four-seamers. Sewald has also abandoned his changeup and sinker and become just a four-seam and slider pitcher, which works when your slider does this.

With a 31.1% CSW on the slider and 39% CSW on the fastball, Sewald has two plus pitches, which have given him a 14.2% SwStr on the season. Both pitches have also allowed tremendously weak contact with an average exit velocity of 84.4 mph on the fastball and 86.7 mph on the slider. So, to sum it up, Sewald is throwing harder and with more rise, which is enabling him to miss bats while also inducing soft contact. That's well, good.

With Kendall Graveman on an expiring contract and almost certainly headed out of town, the time to stash Sewald is now (just don't expect 100% of the saves, as the Mariners have shown that they will use their best reliever in the highest leverage situations, which may not be the 9th inning)

Heath Hembree - RP Cincinnati Reds

Hembree hasn't quite "come out of nowhere" like people claim. The 32-year-old was a very effective reliever for the Red Sox between 2016-2019 until he walked his way out of Boston. I'm being tongue-in-cheek, but as Hembree's strikeout rate grew in 2018, so did his walk rate until he was traded last season, along with Brandon Workman, to Philadelphia. Hembree signed with Cincinnati this offseason and has seen a massive increase in strikeout rate, going from a career 26.1% rate to a 42.1% rate during the season.

A big reason for that has been the slider, which shouldn't be shocking since it's Cincinnati and most of their pitchers seem to make big strides as they master an effective slider. Hembree's slider now is 86 mph and has a 2854 spin rate and 10 inches of horizontal break, whereas the pitch previously was thrown close to 89 mph with a 2600 spin rate and 3 inches of horizontal break. Re-establishing that slider and now throwing it confidently to both righties and lefties has been a game-changer for Hembree, who has shunned his curveball and become a two-pitch pitcher. However, while the slider has an 18.9% SwStr and 34.3% CSW, the four-seam only gets a 9.8% SwStr. It is relying heavily on called strikes and also registers a 5.29 deserved ERA (dERA), which isn't confidence-inspiring.

You can't argue with Hembree's results, and I expect him to remain a key cog in this bullpen for the duration of the season, but with Lucas Sims and Michael Lorenzen coming back, Amir Garrett surging, and possibly Tejay Antone's returning in August, I think there will be too many cooks in the kitchen for Hembree to claim a firm grip on the late-inning role.

Anthony Bender - RP Miami Marlins

Yimi Garcia is almost assuredly being traded. The Marlins have the third-worst record in the National League, and the veteran is on an expiring contract and could be an asset to a contending team. While many assume that Dylan Floro will get the closer gig in Miami, he is also on an expiring contract and is four years older than Bender. So despite Bender's unique path through the independent leagues, the 26-year-old could find himself in a closer gig over the summer. As far as how that came to be, there's not much we can say.

In 2019, Bender was pitching relatively well in High-A for the Brewers but had a strikeout rate hovering around 20%. In his debut season, he has ridden a 97 mph sinker and wipe-out slider to prominence. The slider has a tremendous 21.6% SwStr and 44.6% CSW and, like Hembree, the sinker relies a lot on called strikes.

However, unlike Hembree, Bender's sinker gives up lots of soft contact with a 3.4% deserved hard-hit rate (DHH%) and an average launch angle of just 2.6-degrees, which is why it has a dERA of 0.65. There has been some drop in spin rates since the middle of June, which is something to keep an eye on, but provided that corrects itself, I think Bender can be an impactful fantasy arm for the remainder of the season.

Chad Green - RP New York Yankees

Yes, this includes Green's collapse against the Astros before the All-Star Break. No matter, the 30-year-old has been one of the more impactful non-closer relief pitchers since he was a full-time member of the Yankees bullpen back in 2017. His ability to go multiple innings and sneak his way into a handful of wins and saves has always proved useful only now, he has begun to find himself in the 9th inning more often than in years past. A lot of that has to do with Aroldis Chapman's inability to find the strike zone. In fact, the veteran closer's decline has been more drastic than anything I've witnessed in a while.

Perhaps the 33-year-old has simply lost it or is unable to pitch without "sticky stuff"; however, it's far more likely that he will right the ship in due time. But will it be in New York? He has one more year remaining on his contract, and it's possible that the Yankees could decide to ship him to a contender if they fall farther out of the playoff race.

Even though it's far more likely that he remains, Green should still be on fantasy rosters. The Yankees also have Jonathan Loaisiga to fill the multi-inning role, so Green could remain a factor in the 9th inning until Chapman can figure things out. However, there are a few interesting factors to monitor. Green's O-swing% is the lowest it's been since 2017, and his Z-contact% is up to the highest it's been since 2018. The levels themselves aren't that high, but it's possible that the 2.89 ERA will rise more closer to the 3.51 mark he had last year.

Bailey Falter -Philadelphia Phillies

Falter was a starter for the Phillies all throughout his career and in AAA this year before being promoted, so I fully expect him to transition back into that role. As a result, I don't have much interest in him as a bullpen option because I can't see them making him the closer. He has three offerings with a CSW over 30% and mixes the swing-and-miss of his slider with a solid sinker/four-seam combo. I don't see him as a dominant arm, but he did miss bats in the minors with plus command, so there is something to work with here. If he gets put into a consistent multi-inning role, like Collin McHugh (#2 on this leaderboard) then I think Falter could have some success as a ratios asset for fantasy teams.

Caleb Thielbar - Minnesota Twins

Thielbar has had a rough year on the surface, posting a 4.59 ERA; however, his 3.68 xFIP and 2.90 SIERA are far more indicative of the talent he possesses. His solid K-BB% has endured throughout the entire season because of his plus command and solid 12% SwStr%. He has three pitches - in a fastball, slider, and curve - that all have double-digit SwStr% and CSWs of 27% or better. The issue has been that his fastball has also gotten pounded when it's in the zone.

With the Minnesota Twins having a rough year and likely trading players at the deadline, Thielbar could work his way into the late innings if Taylor Rogers is dealt away. We know that Rocco Baldelli likes to play matchups so the Twins could end the year with some combination of Thielbar and Tyler Duffey or Jorge Alcala as the closer committee. It's something to keep an eye on, and he's a name to add to your Watch List.

Rex Brothers - Chicago Cubs

Brothers is another name to throw on your Watch List. He has experience in the closer role and might be the last man standing if the Cubs decide to trade away Craig Kimbrel, Ryan Tepera, and/or Andrew Chafin, all veterans who are on expiring contracts. Unlike Thielbar, Brothers brings a little heat from the left-side with a 95 MPH fastball that he pairs with a wipe-out slider, which he can just as easily throw for strikes as he can bury it out of the zone.

It might not be a league-winning move, but if Brothers ends up with a share of the closer's role, don't be surprised if he's relatively effective with the gig.

Spencer Patton - Texas Rangers

The Rangers have so many intriguing late-inning relief prospects. Demarcus Evans. Jonathan Hernandez. Joely Rodriguez. All of them have either gotten hurt or struggled in their early MLB experience, which is why the 33-year-old Patton has found himself pitching in the 8th innings of late. Patton has been a journeyman reliever for much of his career, compiling a 5.64 career ERA and 14.6% K-BB%.

There's not a lot to get excited about here, except that Patton gained one MPH on his fastball from years past, which has given him at least an average offering to pair with a solid slider. With Ian Kennedy almost assuredly being dealt at the trade deadline, Patton could work his way into the 9th inning role for Texas, but I wouldn't be breaking the bank to get him as I think he's more of a high three or low four ERA pitcher with a slider that only has a 10.9% SwStr.

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