Coming into the season, the Yankees bullpen was considered to be one of their biggest strengths. Looking at the big picture, the relievers have lived up to expectations, as they currently lead the majors in the following categories: fWAR, FIP, xFIP, K%, and K-BB%. That isn't to say that all is well, though.
Suffice it to say that the bullpen depth has been tested in the early goings. After struggling down the stretch in 2017, Dellin Betances is still searching for his old form in 2018. In addition, Adam Warren and Tommy Kahnle are both on the disabled list, further limiting Aaron Boone's late-inning options.
The Yankees do still have a formidable trio in Aroldis Chapman, Chad Green and David Robertson, but Chapman is a closer only, and Boone can't keep running Green and Robertson out there for multi-inning appearances. The Yankees need another reliever to step up and handle high-leverage situations, and the numbers suggest that Jonathan Holder is their best bet.
The right-hander is coming off a strong and somewhat under-the-radar performance in 2017, in which he threw 39.1 innings and had an above-average ERA, FIP and xFIP. While Holder's ERA is a not-so-great 4.38 this year, his 2.75 FIP is more indicative of how he's pitched overall.
Holder has appeared in 11 games so far, and he's given up runs in only three of them. In fact, all six of Holder's earned runs came in a span of two appearances, his April 3rd clunker against the Rays and his April 6th fiasco against the Orioles. In his other nine appearances, Holder has been spotless — save for an unearned run due to a Gary Sanchez passed ball in the 8th inning of the Yankees' win over Cleveland on May 6th. A couple of horrendous outings have skewed his ERA, but Holder has generally been great this year.
A big factor in Holder's success this year has been his newfound ability to neutralize lefties. Left-handed batters were the bane of his existence in 2017, as he faced them 42 times and allowed them to hit for a .351/.439/.528 line. Holder has been much more successful against lefties this year, keeping them to a .133/.133/.429 line over 14 plate appearances. To put it another way, left-handed hitters have gone from hitting like prime Tony Gwynn against Holder to approximating Adam Dunn's unfathomably bad 2011 campaign. Oh, how the tables have turned.
This isn't just a fluke, either, as there's evidence that Holder is actually executing better against lefties. This is his heatmap against them in 2017:
Notice the red blotch in the lower middle part of the zone, right in the wheelhouse of a left-handed uppercut swing. That's not usually where you want to throw the ball as a pitcher, unless you're tossing batting practice.
Now consider Holder's heatmap against lefties in 2018:
While there are some red spots leaking over the middle of the plate, on the whole Holder has been much better about avoiding the heart of the zone and keeping the ball away from lefties, locating his pitches on either the top or bottom-right corners of the zone. The difference is night and day.
Holder has also tinkered with his pitch mix. In 2017, he was primarily a three-pitch pitcher, using his fastball, cutter, and curveball. This year, he has upped his changeup usage, actually throwing it slightly more than his cutter to date. In addition, he has leaned more heavily on his fastball, going from throwing it 37.2% of the time in 2017 to 50.6% in 2018. He has become a four-pitch pitcher, albeit with more emphasis on his fastball than before.
While from a statistical standpoint it's too early to tell if Holder's new-look pitch mix is driving his recent success, it makes intuitive sense that increased usage of his changeup is allowing him to subdue left-handed batters. According to Holder's player card on Brooks Baseball, his change is “much firmer than usual” and “has slight armside fade”. If he can consistently locate that pitch on the outside corner to lefties - and his heatmap shows that he has - he can miss barrels and generate whiffs and weak contact. That appears to be what he did here, retiring Andrew Benintendi on a particularly nasty changeup to escape a bases-loaded jam. Who said Holder couldn't handle big spots?
Holder has improved against lefties, thereby solidifying his status as a credible relief option for Aaron Boone and the Yankees. This is great news, as the Bombers are currently on the verge of overworking Green and Robertson and could use a few other good arms. I'm not saying that Holder is on the same level as Green and Robertson, but I'm pretty sure he's a cut above the likes of Chasen Shreve, David Hale, and AJ Cole. Boone should entrust Holder with high-leverage situations when he wants to rest Green and Robertson, at least until Warren and Kahnle make their return. Really, he could do a lot worse.