July 8, 2010
The K/BB Ratio
Most of the time when I begin writing or researching an article, the spark comes from seeing something noteworthy on MLB Tonight or in the box scores while checking to see how my fantasy team is performing. At the beginning of the week, Jered Weaver’s strikeout rate piqued my interest, which led to a rather long-winded but informative article on the reason for his vast spike in the rate as well as whether or not it held precedent. Today, the story is a bit different, but along similar lines, as after watching the last couple of innings of Cliff Lee’s most recent start—one in which he issued a walk and whiffed 11 hitters—I could not help but think about his extremely impressive strikeout-to-walk ratio. The guy has walked just six batters in 103 2/3, innings, while striking out 89, leading to a K/BB ratio of 14.83 that, yes, leads the entire sport.
It wasn’t exactly Lee’s ratio that got the motors in my mind churning, however, but rather the actual rate itself. I mean, the rate is used so frequently these days and has essentially been imprinted—no, not imprinted like in the Twilight movies… wait, did I just implicitly reveal I’ve seen all three?—into our statistical vernacular, but can anybody tell me who is credited as its inventor or when its rise to prominence began? I rummaged through my library, re-read most of Alan Schwarz’ The Numbers Game, and even Googled like a madman and still turned up nothing discussing the origin of the rate. It is a perfect example of a number that makes so much sense to use for several different purposes, yet whose origin has somehow managed to elude us. That isn’t to say that knowing the creator or how it was derived is important, but as an analyst it is always interested to learn where stats come from.
The K/BB ratio can be very telling with regards to a pitcher’s peripheral skill set. Used in conjunction with some form of the strikeout and walk rates themselves, either divided by plate appearances or on a per nine-inning basis, the ratio helps complete our view of the periphery. Much like the assist-to-turnover ratio in basketball, the K/BB divides something considered positive by something deemed as negative in order to inform fans, on average, how often a pitcher produces positive results relative to those on the opposite side of the spectrum. Then again, walks might not be the exact opposite of strikeouts, but that is a discussion for another day.
As with the strikeout rate itself, a higher K/BB is better for a pitcher, but the ratio alone does not tell us everything of interest. For instance, towards the end of his career, Greg Maddux consistently posted K/BB ratios of 4.0 or higher, a fantastic mark, but one derived from an extreme dearth of free passes issued and not necessarily borne out of frequent swings and misses or caught lookings. This does not invalidate his rate in any way, but it does shed light on how the ratio can manifest itself in different forms. Some pitchers, like Phillies left-hander Cole Hamels this season, have produced very solid rates bordering on three punchouts per each walk but with higher inputs on both fronts. Others, like teammate Jamie Moyer, aren’t missing many bats, but prove so stingy with the walks that the end result is similar.
Another interesting bit of tid when discussing the K/BB ratio is that it is usually better to use UBB, unintentional walks, as the denominator, because IBBs are not the result of anything skill-based from the pitcher, and are rather initiated by the manager. Why then should we judge a pitcher’s peripheral numbers—used primarily to evaluate what he can control—by something he can’t control, aside from somehow convincing his manager to go back to the dugout with a changed mind?
Getting back to Lee, where would his K/BB ratio rank if the season, for whatever reason, ended today? Slight tangent—when did people start thinking along those lines? Was there ever a time when a season just randomly and unexpectedly ended? Anyways, across pitchers with 100 or more frames logged in a season, Lee’s 14.83 K/BB ratio would rank … first … ever, and it isn’t particularly close. Even if we remove intentional walks from the denominator, Lee’s mark would still top all competitors with the same innings pitched restriction. Looking at all such pitchers leading up to our current year, the table below houses the top strikeout-to-walk ratios over the last half-century with a 150 IP minimum:
While Silva’s season is still one of the oddest in recent memory and Sheets’s was primarily the byproduct of the largest jump in strikeout rate after an established rate over three years, the rest of the list reads pretty much like a who’s who list of pitchers with tremendous control who could also put batters away without allowing a ball in play. Extending out to the top 20, names like Randy Johnson, Roy Halladay and Juan Marichal join the party as well. But what if we remove intentional walks from the equation? Does anyone shift?
When intentional passes are removed, not only does Maddux’s 1997 season overtake Saberhagen’s for the single-season lead, but his 2001 and 1996 seasons go from out of the top ten to third and fifth place, respectively. Using unintentional walks is usually a better sign of what the pitcher will control moving forward, though it could certainly stand to reason that a manager may exhibit similar tendencies year after year. Either way, the highest such rate is still lower than Lee’s current mark of 14.83, and while the Cliffer—that’s what we call him in the ‘biz—might not sustain a rate so high, it is truly hard to imagine a pitcher as locked in as he is right now imploding to the tune of even a 6.5 K/BB ratio over the rest of the season.
At the beginning of the season we marveled at how Halladay might win 27-30 games or how Ubaldo Jimenez might post an ERA under 1.50, but the one feat that could still come to fruition is Lee’s quest for the best single-season K/BB ratio of the Retrosheet era.