Fun With Reliever Leaderboards

At some point over the last calendar year, we added K%-BB% in our advanced stats tab. It appeared without warning, and I’ve been using it ever since. The statistic captures pitcher dominance in a way that can be lost using K/BB. For example, Aroldis Chapman’s 4.42 K/BB is good (25th among qualified relievers). His 40.6 percent K%-BB% ranks first by over five percent.

Does this matter, or is it an example of torturing numbers to fit a narrative? In 2012, Glenn DuPaul found that K%-BB% was better at predicting success than ERA estimators. Eno noted that it takes about 150 batters faced before we’re looking at more signal than noise.

So we’ve identified an alternative to ERA estimators for predicting future performance. Today we will explore the K%-BB% leaderboards split by batter handedness. Rather than embedding a heap of information or creating a cutoff, I’m just going to link out to the two leaderboards (click the headings). I’m using a low 10 innings pitched threshold so relievers aren’t excluded. That means we need to be wary of sample size.

Against Left-Handed Hitters

As you might guess, the best K%-BB% rates against left-handed hitters mostly come from fellow southpaws. Unsurprisingly, Chapman takes the crown with a ridiculous 51.2 percent K%-BB%. Overall, he struck out 58 percent of lefties. Andrew Miller ranks second after his glorious breakout season with 43.9 percent K%-BB%.

The first righty on the list is Indians closer Cody Allen who ranked fifth with a healthy 35 percent rate last season. Other righties in the top 15 include Dellin Betances, Craig Kimbrel, David Robertson, Brad Boxberger, and Steve Cishek. Will Smith, ranked sixth, is the first pitcher who doesn’t look the part of a closer. Chris Sale is the only starter in the top 15, although Madison Bumgarner (17th) and Clayton Kershaw (19th) aren’t far behind.

In most cases, this information isn’t particularly useful. We knew most of these pitchers are fantastic. The real value to this leaderboard is for holds leagues where a dominant lefty specialist can rack up cheap holds and amazing peripherals. Guys like Smith, Jake Diekman, and Charlie Furbush can flourish in the right role. While they’re unlikely to fill in as closers, they can help in any league as waiver wire streamers.

Against Right-Handed Hitters

Only a handful of lefties appear on the first page of the leaderboard, namely Chapman, Sean Doolittle, Miller, and Kershaw. All four ranked prominently against their fellow southpaws too. A few righties also appear on both lists, including Boxberger, Ken Giles, and Betances.

If you were lining up to take Kenley Jansen as the best reliever against righies, come collect your prize. His 40.4 percent K%-BB% was best in the league. He’s followed by Wade Davis (37.8 percent), Chapman (37.7 percent), and Jose Fernandez (37.4 percent). To see a starter so high on the leaderboard is impressive.

A few names require more research. Dylan Axelrod ranked 15th, but he features some strange numbers and hefty splits in his tiny 18.1 inning performance. The Rangers might have a great ROOGY in Phil Klein. In a tiny sample, he crushed right-handed competition (47 batters faced, .152 wOBA) only to be crushed in turn by lefties (32 batters faced, .492 wOBA). Fernando Salas posted pedestrian numbers against lefties, but he clamped down on walks versus fellow righties while posting a 31 percent strikeout rate. Salas might be somebody worth targeting for the occasional inning, but I would stay away from the other two.

Parting Thoughts

As you dig deeper into both lists, you’ll find a few sleeper candidates for a fantasy bullpen role. Indians lefty Nick Hagadone stifled both types of hitter in about half a season. He was used situationally last season, but he may be ready for a full inning role. Tony Watson was good against right-handers and looks like the early season backup to Mark Melancon. Right-hander Joel Peralta ranked 35th against left-handers last season; his struggles came at the hands of righties. A glance at his splits data reveals the potential for a full recovery from his 4.41 ERA. For now, he’s probably the primary setup man to Jansen.