How much has Jordan Montgomery actually worn down?

This season hasn't been short on pleasant surprises, and among the best has been the sudden emergence of Jordan Montgomery. The big left-hander has been instrumental so far, ranking second on the team's pitching staff in WAR. Yet it goes without saying that even as important as he's been, he appears on the verge of losing his rotation spot.

Montgomery has struggled recently, with several of his worst starts coming over the last month. With the Yankees importing veterans like Sonny Gray and Jaime Garcia, the team now has six capable starters. The odd man out would seem to be Montgomery, as his poor recent performance has led many to posit that the rookie has worn down during his first run in the bigs.

That Montgomery is worn out feels like a simple and natural conclusion. His results, in terms of runs, have been much worse of late. Moreover, there's one fact that lends major credence to the idea that Montgomery is tired: His velocity is down. After peaking at an average of 92.6 mph on his four-seamer in June, Montgomery's velocity dropped to 91.9 mph in July.

It would probably be easiest to look at the heap of runs Montgomery surrendered in July, as well as his subsequent velocity drop, and sleep soundly knowing that he has worn down. So let's take the more challenging route, and see if there's any evidence to the contrary. Has Montgomery actually held strong as the season progressed?

Just looking at his run prevention numbers, Montgomery’s results have gotten worse. Yet runs allowed isn’t the only result pitchers produce. Runs are the most important variable, but pitchers also are trying to miss bats, deceive hitters, and limit quality contact. Just because Montgomery's ERA looks worse doesn't mean his other numbers have also declined. If his underlying results look better than his ERA, then perhaps we have reason to believe he hasn't worn down all that much.

The best thing a pitcher can do is prevent his opponents from actually hitting the ball at all. We've already established that Montgomery's velocity has slipped a bit, and less velocity typically makes it harder to miss bats. Even so, here's Montgomery's 15-game rolling average swinging strike rate and contact rate, courtesy of FanGraphs:

There has virtually been no movement in Montgomery's ability to generate whiffs. He was great at missing bats when he initially came up, and he has remained so even as his ERA inflated.

As vital as producing swings and misses is, there are of course other elements of pitching, like suppressing damage on batted balls. If Montgomery was wearing down and giving batters more hittable pitches, we should see a notable difference in the quality of contact allowed. That too doesn't seem to be the case:

The top line represents his groundball rate, which has escalated as the season has worn on. The middle represents his hard contact rate, which has slightly increased. Lastly, the bottom represents soft contact rate, which has also modestly increased. For the most part, Montgomery's batted ball profile has adhered closely to his overall norms.

In fact, it actually appears that Montgomery’s recent contact allowed is notably weaker. Baseball Savant's expected wOBA estimates Montgomery should have seen a wOBA allowed of just .284 in July. That figure was actually higher across the three months prior, at .302. Take a fancy new metric like xwOBA with a grain of salt if you will, but there's still reason to believe that Montgomery hasn't been hit hard across his recent starts.

Outside of his small velocity drop, there just isn't much evidence that Montgomery has been a demonstrably different pitcher later in the season. That velocity can’t be hand-waved away, and Montgomery has given up plenty of runs in July. That being said, if Montgomery keeps pitching like he has, it's unlikely he will continue to give up runs at this rate.

This doesn't make the Yankees' decision any easier. Montgomery is a rookie whose career-high in innings is a handful of starts away. The team also has plenty of veteran starters that simply need turns in the rotation. He also has been one of the team’s best pitchers, and a trip to back to the minors doesn’t seem like an adequate reward for such performance. Regardless, if Montgomery makes a few more starts, it would be reasonable to expect positive regression. If he doesn’t, then the Yankees will be thrilled with what he unexpectedly gave them as a rookie.