For the Yankees to surprisingly contend this year, they needed players to put in some surprising performances. That was especially true regarding the pitching staff, as there was plenty of consternation about the rotation's depth all offseason. So far the rotation has performed well, posting a 3.93 ERA as a group to go along with an 8.75 K/9 rate.
In order for that to happen, they needed mercurial pitchers like Luis Severino and Michael Pineda to be the best versions of themselves, as they have. It was also necessary to find someone to fill the vacancy at the back of the rotation, and that is what Jordan Montgomery has done capably.
The Yankees haven't asked Montgomery to be anything other than a serviceable back-end starter. On the surface, that is precisely what he has been. His middling 4.15 ERA is befitting of a solid number four or five starter. He's struck out a batter an inning, but he's also lived with runners on base. He's allowed 33 baserunners in his 21.2 major league innings.
Go a bit deeper than that, though, and you might find reasons to be more excited about the young hurler. As a big left-hander who doesn't light up the radar gun, the ways Montgomery impresses aren't obvious. He has, however, done a few things at a very high level during this young season. For one, he boasts a deep repertoire that may help him deceive opposing hitters. There isn't a catch-all metric for deception, though Baseball Prospectus' pitch tunnels research is a fascinating foray in that direction.
Another way to try to capture deception is to look at the rates at which opposing batters swing at pitches in and out of the zone. If an opposing hitter is having trouble pinning down what's coming from the pitcher, intuitively, the hitter should have a harder time judging whether to swing, which can lead to more swings at bad pitches and fewer at hittable ones.
Montgomery has excelled in this area. Per FanGraphs, he has generated the seventh-highest rate of swings on pitches out of the zone among pitchers with at least 20 innings this year. His in-zone swing rate of 63% is also well below league average, meaning opposing hitters generally aren't swinging at strikes against Montgomery. They are, however, chasing balls frequently.
Is this apparent deception a result of Montgomery's deep stable of offerings? It's difficult to say. His repertoire of pitches is another reason to be impressed, as he appears to have several legitimate weapons with which to attack hitters.
Coming up through the Yankees’ system, one of Montgomery's strengths was his ability to use a variety of pitches. That ability has arrived with him in the majors. According to Brooks Baseball, Montgomery has used a four-seamer, two-seamer, slider, changeup, and curveball all at least 15% of the time, but none more than 22% of the time.
More importantly, those pitches he so evenly utilizes have made hitters swing and miss. Batters have whiffed on about one-fifth of their swings on his fastballs, an above average rate for a starter. They've also whiffed on over half their swings on his breaking pitches, as well as 40% of their swings on his change. I is tremendously rare for a pitcher to posses, use, and generate whiffs with five distinct pitches.
It's also why Montgomery has posted some of the best overall whiff rates in the game. Again among pitchers with at least 20 innings pitched, Montgomery has the fifth-highest swing strike rate, one spot behind Max Scherzer. His contact rate is the seventh-lowest among that group, just behind noted strikeout artists like Chris Sale and Danny Salazar.
Returning to surface level numbers, things aren't quite as pretty. Montgomery has allowed hits on seven of 13 batted balls yielded with his two-seamer. Batters are also hitting .381 with two home runs against his four-seamer. There could be some batted ball luck in play here, however.
Baseball Savant's new expected batting average metric calculates the average a pitcher would be expected to allow based on the quality of contact he's yielded. It suggests Montgomery *should* have allowed a .311 average on his four-seamer, compared to the relatively higher mark he’s allowed in reality.
If you look just at the runs and baserunners Montgomery's allowed - simple measures which undeniably are important - he hasn’t entirely stood out. I think a greater level of optimism regarding Montgomery is reasonable considering the way he ranks among the game's elite in terms of deceiving hitters. The Yankees never asked Montgomery to be more than a fifth starter. If that's all he amounts to, they'll be pleased. If he continues to baffle hitters with five different pitches, he has a chance to be much more.