Since each of these new Brewers pitchers throws a splitter, it is worth investigate the elements that create an effective splitter. First, one can question which aspects are the most important for a splitter: for instance, is success with a splitter evident in swings-and-misses, groundballs allowed, flyballs prevented, or some combination? These questions can be answered via the BaseballProspectus PITCHf/x leaderboards. For the following study, I first looked at starting pitchers that threw 200 or more splitters all-time, and I specifically considered Total Average against (TAv), swing percentage, whiffs per swing, groundballs and flyballs per Balls-In-Play (BIP), and pop-ups per BIP and fouls per swing.

First things first, here are the most effective splitter TAv for starting pitchers. I took the Top 11 (because Hisashi Iwakuma was #11, and I’ve previously looked at an Iwakuma / Guerra comp), and then added some other interesting pitchers (more on that below):

In order to judge the effectiveness of these pitchers’ splitters, I attempted to isolate contact results that could suggest lack of effective timing by batters (such as foul balls or pop ups), potentially effective BIP results (more groundballs than flyballs, ostensibly keeping the ball in the ballpark at a higher rate), and causing batters to fail to make contact. I also including swing percentage, since one might argue that a splitter is ineffective if the batter recognizes it as a ball outside the zone, or an off-speed / breaking pitch. This first step is to attempt to build an anecdotal body of evidence about the splitter.

Swings and whiffs:
In terms of drawing swings and drawing whiffs, several of the most effective starting pitchers (Top 10, or Top 20 percent) in terms of splitter TAv also drew high swing percentages and/or high whiff percentages. Junior Guerra, for instance, is successful with the splitter almost solely due to his ability to draw whiffs.

This should not necessarily be a controversial suggestion about the splitter. First, the splitter needs to draw swings in order to fool the batter; it’s not necessarily a set-up pitch like a fastball, or even a cutter or tight breaking pitch (or a get-me-over curve, for that matter). Furthermore, if a pitcher is drawing a high percentage of whiffs on a pitch, that limits the chances that a batter has to induce damage. Below, one will see that Guerra is absent the groundball, flyball, popup, and foul ball leaderboards; in fact, his batted ball and contact numbers on the splitter are positively pedestrian. But, since Guerra draws a whiff nearly 41 percent of swings on his splitter, he maintains strong odds of success with the pitch.

Groundballs and flyballs:
Notably, the most effective splitter pitchers are absent the top of the groundball and flyball splitter lists. Below, I’ve provided the top 25 (nearly Top 50 percent) of groundball and flyball splitter pitchers, presenting the best TAv pitchers in bold. I’ve added extremely interesting pitchers in italics, specifically those who managed to pitch in the Top 10 of groundball and flyball results without landing in the Top 10 splitter TAv. This means that these pitchers yielded arguably preferable groundball / flyball performances without producing elite TAv against on their splitter.

The implication here is that the splitter is not a “weak contact” pitch. A pitcher may not necessarily look to the splitter to induce a groundball, or prevent a flyball. This hypothesis is drawn from the fact that the very best splitter TAv pitchers do not necessarily exhibit these desirable batted ball traits, meaning that their splitters are not necessarily effective because of their groundball / flyball ratios. Tsuyoshi Wada, Alex Cobb, Nathan Eovaldi, and Taijuan Walker are the outliers worth studying here.

Pop Ups and Fouls:
Like groundballs and flyballs, so too with pop ups and foul balls: once again, it does not appear that a great splitter is great because of its ability to induce weak contact.

I toyed with combining whiffs per swing with foul balls per swing, in order to create a quick-and-dirty hybrid stat that accumulates the trickiest splitters: the ones that cause batters to swing and miss, or make mistimed contact a solid percentage of the time. But Guerra is once again instructive here, as he would perform very well in this statistic because of his high strike out rate. In this case, a “Power/Speed Number” method employing the harmonic mean could find the most balanced and effective timing-limiting splitters (using a formula such as [(2*FoulSwing*WhiffSwing) / (FoulSwing + WhiffSwing)]).

Judging the new Brewers righty splitter tossers, then, one might hypothesize that focusing on the ability to induce swings and whiffs is indeed much more important than focusing on splitter-induced grounders, flyballs, fouls, and pop-ups. This may seem like an obvious conclusion, but it is worth investigating the PITCHf/x results in order to verify the assumption. In this sense one might also be able to form accurate expectations for this gang of Brewers acquisitions.

Stuff Quality
The benefit of having PITCHf/x data available is that one can compare how splitters move compared to the other major pitches in a pitcher’s arsenal. This is another qualitative investigation of a pitcher’s splitter production, as one could conceivably compare horizontal and vertical movement variations, as well as spin rate and velocity differentials, in order to determine why the best splitter TAvs are indeed the best.

With this stated, here is the list of the notable right-handed starting pitchers analyzed above. I drew information from Brooks Baseball, isolating a pitcher’s primary fastball or sinker and main breaking pitch against the splitter. This essentially builds a basic game whereby one can understand how the splitter is used:

• Is it a “true change of speed” (slower than the breaking pitch AND fastball) or is it a “stepping stone” between the fastball and breaking ball?

• Does it primarily move armside or gloveside compared to both the fastball and breaking pitch?

• Does it primarily “rise” or “drop” compared to the fastball and breaking pitch?

• Perhaps most importantly, what are the other pitches that a successful splitter ball pitcher throws? One should not rule out that a pitcher’s other offerings make a splitter great, or amplify the effects of a splitter, and one should not assume that a pitcher’s splitter produces great results only because it is a great splitter on its own. (This may seem obvious, but it is worth arguing that a pitcher’s arsenal is a comprehensive whole, and not simply a sum of parts).

What does this mean? A few observations:

• The splitter is almost universally paired with the slider. This is fascinating in and of itself — baseball has a tradition of “we stick together” arsenals, meaning that pitchers work with what is tried and true. For as rare as splitter pitchers are in the MLB, it is surprising that so many of the best splitter pitchers have comparable breaking pitch offerings.

• Only six of the best splitter pitchers use the offering to break further armside against their fastball, meaning that the pitch would break further inside against a right-handed batter. Six of the best splitter pitchers (including Guerra) feature a split that breaks more than 1.5″ gloveside against the fastball, or “away” from a right-handed batter.

• Everyone except for Masahiro Tanaka throws a splitter that breaks further armside (“in” on RHB) compared to their breaking ball. The vast majority of great splitters also “rise” compared to a breaking ball; obviously since pitches don’t actually “rise,” one might more effectively say that this is an optical / perceptual tool that allows a pitcher to play the breaking ball against the splitter, since they “drop” in different manners (the breaking ball much more, the splitter much less).

• Some pitchers have “equidistant” horizontal and vertical ranges between their fastballs and breaking balls, when compared with their splitter. For example, take Guerra, who uses a split that “drops” 5.67″ from his fastball, but “rises” 5.27″ from his slider. Similarly, his split breaks to the gloveside by 1.93″ against the fastball, but moves armside by 2.26″ against the slider. So, one can see that Guerra aids his 94 / 86 / 83 fastball / split / slider stepping stone with vertical and horizontal planes that differentiate the pitches in a harmonic manner. Jose Contreras, Yu Darvish, and Kevin Gausman exhibit some similar harmonies, although not necessarily to the extent of Guerra.

• What surprised me the most is that the pitchers are evenly divided in how they use the splitter in their velocity range; approximately half of the arsenals use the splitter as a bridge between the breaking ball and fastball, leaving the others to use the splitter as a true change of speed. Some of these pitches move into semantics, as pitchers like Jose Contreras probably threw a “forkball,” Tim Lincecum probably uses a “vulcan change up” variation, and Mat Latos throws an unclassifiable oddity.

• Interestingly enough, having a top TAv against on a splitter does not always require a blazing hot fastball. In fact, some of the most effective splitter pitchers paired that offering with another moving fastball option, such as Roy Halladay’s gang of darting sinker-cutters, Dan Haren’s cutter, and a handful of other effective sinker pitchers (including “old” splitter pitchers like Ryan Dempster or Hisashi Iwakuma).

There is not a clear arsenal for success for projecting an unknown splitter pitcher into stardom, although one can suggest that using the pitch to elicit whiffs is much more important than any other outcome. The next question will be, “how do the new Brewers fit into these hypotheses?”

• Guerra made his first MLB start in his age-31 season.
• The righty was one of the “quietest” no-risk moves made by GM David Stearns during the offseason, and represents “pure reward” for the Brewers.
• Guerra profiles as a potentially high-strikeout master on the mound.
• Even better, rather than following a traditional secondary pitch sequence (relying primarily on a slider or curveball), Guerra joins a group of pitchers that chooses from the change / fork / split / screwball spectrum for their major neutralizing pitch.
• As BPMilwaukee’s own Jack Moore documented, splitter is something else. In a rebuilding season, it represents an excellent aspect of the game to cheer on (much like Ben Sheets’s 2004 curveball).
• Better yet, the rookie is having quite a good start to his season, which is a breath of fresh air within a struggling rotation.

Most analysis of Guerra justifiably focuses on the righty’s splitter. The pitch features a steep, dramatic drop that gives him a chance to wipeout batters. BPMilwaukee’s own Ryan Romano also detailed how Guerra uses pitch sequencing to improve the impact of his main off-speed offering. Yet, fans should arguably be focused even moreso on Guerra’s age, as the righty is (thus far) poised to accomplish a one-of-a-kind season in MLB’s divisional era: Guerra has the opportunity to start the largest slate of games ever pitched by a hurler debuting as a starter during their age-31 season.

Since divisional play began in 1969, 1236 pitchers have worked during their age-31 season. It has been quite rare to debut as a starter at age-31, however. The first divisional era age-31 starting pitching debut was made by Oscar Zamora for the 1976 Cubs; Zamora started 2 of 40 games that year, having worked as a reliever in 1974 and 1975 for the Lakeview Nine. Prior to reaching the MLB in 1974, Baseball-Reference shows that Zamora spent a decade working through the minors, mostly in the Eastern League and American Association. The Cubs purchased Zamora out of the Astros’ system, and the righty even served as a relatively early free agent in the MLB (1977).

Zamora’s experience is rather standard among age-31 starting pitching debuts: he didn’t start another MLB game after his age-31 season. For example, the Brewers had their own age-31 starting pitching debut in 1987 with Mark Clear, a quality reliever acquired prior to 1986 via trade (and re-signed prior to 1987). According to The Neyer / James Guide to Pitchers, Clear was a curveball-first pitcher who also developed a slider in Milwaukee. In his June 30 start in 1987, Clear posted his roughest outing of the year, facing the stacked Tigers offense at County Stadium in what would become his only MLB start.

Fourteen total pitchers have made their first MLB start during their age-31 season during the divisional era (including Guerra), and nine of 13 failed to make another MLB start after age-31. Guerra’s feat is exceptionally rare, and the track record of age-31 starting pitching debuts leads one to wonder how to project Guerra’s future potential.

Recent age-31 debuts in the form of International Free Agents provide more tantalizing comparisons for Guerra. Jose Contreras signed out of Cuba as an amateur free agent in 2003, claiming nearly 100 games pitched in the Cuban National Series. Almost a decade later, Hisashi Iwakuma signed as a free agent with the Mariners, having pitched for 11 years in the Japanese Pacific League. Alongside swingmen/set-up men/journeymen Darren Holmes and Al Levine, Contreras and Iwakuma have the most post-31 experience in the MLB from this group. These international players also have the best track record, as Contreras posted five better-than-average cFIP (50.0 IP+) seasons in his career, while Iwakuma has served within a bona fide 1-2 punch in Seattle.

In some sense, Iwakuma’s ascent and Contreras’s fluctuations offer two realistic poles for discussing Guerra’s potential. First, like Contreras, one must note that the Brewers righty can be a serviceable pitcher and work through some hiccups in his career; it doesn’t have to be a fairy tale for Guerra to help Milwaukee. Second, like Iwakuma, one must consider the benefits of a strong off-speed pitch and good peripheral performance for Guerra. Thus far, Guerra’s biggest question mark remains his groundball:flyball ratio, although the righty arguably limits the damage with his strong strike out and walk rates.

Perhaps most interestingly, Guerra’s arsenal almost perfectly mimics that of Contreras and Iwakuma in general orientation toward the forkball / splitter spectrum. To be fair, there is no confusing Contreras’s knuckling, tumbling soft fork with Guerra’s hard-slicing variation. The general point is that it is a fascinating accident of history that two of the most successful arms from the age-31 starting debut group share the same basic pitching profile for their most popular offspeed pitch (neutralizing “split / fork” spectrum, instead of breaking “curve / slider” spectrum).

[Incidentally, while digging through seasonal data, another interesting splitter profile emerged in an age 31 season: Ryan Dempster made an astonishing role change from closer to starter in 2008, during his age 31 season, and he also became a serviceable (or better) starter thanks to a fastball / splitter / slider general profile. Mike Marshall also produced his unbelievable 208.3 IP relief season as a screwball wielding 31-year old, adding to a pre-splitter version of this “neutralizing” profile. Mike Scott is another obvious age-31 breakout comparison with the split, and Scott produced several solid seasons after his elite breakout.]

Although pitch f/x data was not available for Contreras’s debut, the righty thankfully snuck within the publication timeframe for the Guide to Pitchers by Rob Neyer and Bill James. Later Brooks Baseball entries confirm that Contreras’s forkball was his slowest pitch, and in some successful years (like his 2008 87 cFIP season) the righty equally selected his sinker, slider, and fork. While some of Contreras’s command woes are instructive for Guerra’s path, so too is that veteran’s shift to equal pitch selection (or pitch sequencing development). One might expect Guerra to adjust toward his fastball and slider to keep hitters guessing as the season moves on and scouting reports circulate. This adjustment could be necessary to improve that groundball rate.

In the worst case scenario, Brewers fans are treated to a truly historical campaign in 2016, and that’s the highlight for Guerra. Contreras worked nine MLB starts in his debut season, while Iwakuma reached 16; if Guerra keeps his rotational spot and remains healthy, he stands a good chance of starting the most games of any age-31 starting pitching debut during the divisional era. This is a thrilling feat that scores one for the “age ain’t nothing but a number” camp.

In the best case scenario, the righty remains in the rotation, and continues to serve as a serviceable-to-surprising option. Obviously reality offers several notches between those poles, from a value-seeking trade to potential relief roles (unleashing Guerra’s split in short stints could catapult the righty to poor man’s Eric Gagne status, for those that remember the diving “vulcan change”). At any rate, don’t get sick of the hype and coverage, embrace it: this journeyman could produce a rare career arc, and it starts here.

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BaseballProspectus. BaseballProspectus, LLC. [for advanced stats & Brooks Baseball.]
Baseball-Reference. Sports-Reference, LLC. [for historical data]
Rob Neyer and Bill James. The Neyer / James Guide to Pitchers. New York: Fireside, 2004.