Few things can undo an otherwise-solid relief pitcher quite like a strong platoon split. The ability to set down opposing hitters regardless of handedness will separate the middle relievers and closers from the LOOGYs (and ROOGYs). Of the many relief pitchers that currently don the Brewer blue, Michael Blazek stands out as arguably the most indiscriminate, whereas Jeremy Jeffress has struggled somewhat in this area. If the latter hurler adopts the approach of the former, though, he could take a step forward.
Let’s start with Blazek, who cut down anyone the opposition threw at him in 2015. He limited lefties to a .243 wOBA and righties to a .252 wOBA en route to a 2.43 ERA and 2.46 DRA over 55.2 innings. That even dominance may come as a surprise, given Blazek’s four main pitches:
| Fourseam% | Sinker% | Slider% | Curve% |
|---|---|---|---|
| 32.8% | 13.0% | 26.5% | 27.6% |
According to research from Max Marchi, fastballs, sinkers, and sliders generally have very large platoon splits. In other words, they’ll fool same-handed batters but won’t fare well against opposite-handed ones. Relying on that trio for nearly three-quarters of his pitches would thus leave Blazek vulnerable to left-handed batters — unless he changed his pitch mix depending on the situation:
| Handedness | Fourseam% | Sinker% | Slider% | Curve% |
|---|---|---|---|---|
| L | 28.0% | 24.6% | 9.0% | 38.1% |
| R | 36.6% | 3.9% | 40.1% | 19.4% |
Marchi’s research also showed that curveballs — especially those with a lot of movement, like Blazek’s — will tend to put up a reverse platoon split, meaning they’ll succeed against hitters who swing the other way. Recognizing that, Blazek doubled his curveball rate against southpaws, which allowed him to remain effective against them.
We’ll now move to Jeffress. While he pitched fairly well for the Brewers this year — with a 2.65 ERA and 3.78 DRA in 68.0 innings — lefties gave him some trouble. They posted a .314 wOBA in 104 plate appearances against him, significantly higher than the .276 mark righties notched in their 181 trips to the dish. Nor did this start in 2015: Before this year, Jeffress had held right-handed batters to a .308 wOBA but had sacrificed a .341 wOBA to left-handed batters.
Unlike Blazek, Jeffress doesn’t own a slider; Jeffress’s three primary pitches — the four-seam fastball, the sinker, and the curveball — occupied a respective 23.7 percent, 53.7 percent, and 21.0 percent of his arsenal in 2015. Those two hard offerings lend themselves to a platoon split, and the manner in which Jeffress deployed them only made matters worse:
| Handedness | Fourseam% | Sinker% | Curve% |
|---|---|---|---|
| L | 19.4% | 50.9% | 25.3% |
| R | 26.3% | 55.3% | 18.4% |
Jeffress threw his curveball a bit more often when facing left-handed hitters, but he didn’t spike its usage like Blazek did. Perhaps uncoincidentally, Jeffress didn’t experience the joy that comes from retiring all kinds of batters.
The curveball certainly seems to work against lefties, who whiffed 21.4 percent of the time they saw it this year. That ability makes sense: As a heavily-running curveball — its seven inches of horizontal movement ranked 12th out of 61 relievers — it should retain its efficacy versus southpaws. Jeffress possesses an offering that can neutralize the platoon splits of his four-seamer and sinker; he just has to follow in Blazek’s footsteps.
Jeffress doesn’t have a massive platoon split (he’s no Will Smith). Even if he continues to implement his pitches as he did in 2015, he likely will hold his own against any sort of opposing hitter. With that said, he probably won’t take his game to Blazek’s level without shifting his strategy. The road to becoming a top-notch relief pitcher runs through a lot of lefties, whom Jeffress can easily take down — so long as he learns from his teammate.