Back in the spring, there was a gaggle of starting pitchers under consideration for the final spot in the Yankees rotation. Eventually, the lesser-known starter who wowed management got the chance. Jordan Montgomery has been a top-five rookie starter this year so far and, by all accounts, looks like a major leaguer. Now, the question has shifted. Now, we ask not “Will he pitch in the majors?” but “How good will he be?”

Before the season began, I asked Eric Longenhagen about the pitcher, and based on when he’d seen him last, the ceiling seemed low:

Eric Longenhagen, while appreciating the improvement in the slider, still thought that the pitcher “lacks a true swing-and-miss secondary.” I’m not sure “Montgomery’s command of a diverse pallet of junk should allow him to negotiate through big-league lineups multiple times” is a booming recommendation.

Montgomery certainly has five pitches that he throws regularly, and three of those pitches are non-fastballs, which you could call junk. But are they any good? Let’s take a look at his arsenal through the lens of the movement, spin, and velocity data that has been shown to be relevant.

Jordan Montgomery Pitch Percentiles Pitch Spin Movement Velocity Four-Seam 73 92 43 Curve 28 45 60 Slider 81 55 Sinker 11 50 Change 3 11 SOURCE: Baseball Prospectus / Statcast Movement and velocity percentiles based on research on changeups curveballs , and sliders linked here. Velocity percentiles limited to lefty starters this year. Movement for secondaries defined off of the four-seam fastball.

A few things stand out here. Like, Montgomery is a fastball/breaking-ball guy, first of all. The sinker and the changeup aren’t good, even if they’re getting good results in a small sample. They can maybe work as “show-me” pitches, but they don’t measure up to other pitches in terms of velocity and movement.

But he has his strengths, too. His fastball has tremendous ride, born of an over-the-top release, and though the velocity is middling, it has good spin and looks like an above-average pitch. The curve has ups and downs but looks about average on sum. Strangely, his newest pitch, the slider, looks like his best pitch, with plus drop compared to his rising fastball and good velocity to boot.

So Montgomery throws five pitches. Two are below average, but he doesn’t throw them a ton. His curve is average, and his bread-and-butter pitches, the four-seam and slider, are above average to plus. You’d be tempted to call him an above-average, a mid-rotation guy, and call it quits — except that we lack some perspective on how these things come together.

In order to gain at least some of that perspective, I thought it would be good to compare this four-seam/breaking-ball lefty to the best four-seam/breaking-ball lefty in the league using the same rubric. You might have heard of Clayton Kershaw.

Clayton Kershaw Pitch Percentiles Pitch Spin Movement Velocity Four-Seam 73 99 71 Curve 34 98 4 Slider 24 96 Change 3 36 SOURCE: Baseball Prospectus / Statcast Movement and velocity percentiles based on research on changeups curveballs , and sliders linked here. Velocity percentiles limited to lefty starters this year. Movement for secondaries defined off of the four-seam fastball.

The four-seam is better for Kershaw! The curve is better, though different. The change is just as bad! The slider is better for the Dodger, probably.

Wait, just probably? Doesn’t Kershaw have one of the best sliders in the game? Not necessarily, it seems. He certainly did have one of the best sliders. Over the last year, though, something weird happened to it. It got harder and lost drop, and has lost many of the whiffs in the meantime, too, as Chad Moriyama so ably pointed out.

Let’s go to the tape. Clayton Kershaw’s current slider:

Jordan Montgomery’s current slider:

I might take Montgomery’s. Blasphemy, maybe, but we know from the analysis here that the Yankee’s slider has more movement now (with above-average velocity), and that movement is slightly more important for whiffs than velocity for sliders.

That’s okay, our world view need not collapse around us. It’s still true that Kershaw’s fastball and curve are superior. There’s also the big asterisk that hangs on every analysis of a pitcher ever: command. We don’t have a great number for command, but we are all pretty sure that Kershaw has the best command in the league.

We think that Montgomery has good command! Look back on Longenhagen’s tepid early-season endorsement, and Montgomery’s walk and homer rates in the minor leagues, and most subjective appraisals, and you see mentions of good command.

And if it bears out that Montgomery truly has that command, despite early-season walk-rate hiccups — based perhaps on becoming more comfortable with that good slider — then we’ve got quite a pitcher on our hands. After all, “not quite Clayton Kershaw” is an epithet most pitchers in baseball would gladly accept.