What we know and don’t know about Nick Rumbelow

I was listening to the latest episode of The Wheelhouse yesterday and was fascinated by Jerry Dipoto’s discussion of spin rate. (You definitely need to start listening if you haven’t already.) He used Nick Vincent as the primary example of a pitcher who generates outstanding spin rate on their fastball to out-produce what might be expected based on a pitch’s raw characteristics. We’ve known for a while that the Mariners have targeted pitchers with “rising” fastballs—more specifically, high-spin four-seam fastballs—so to hear it straight from Dipoto’s mouth was a nice confirmation. A number of times during the conversation, Nick Rumbelow’s name came up as Dipoto discussed some of the other pitchers he’s targeted with impressive Statcast numbers.

Of course, the first thing I did was go straight to the data source. Rumbelow made his only major league appearances in 2015, the first year Statcast was implemented across all of baseball. I queried Baseball Savant’s database for the spin rate on his fastball and curveball and was surprised by what was returned. Among the 483 pitchers who threw at least 100 four-seam fastballs in 2015, Rumbelow’s spin rate ranked 464^th, with an extremely low 1971 RPM. His curveball wasn’t much better, ranking 338^th out of 349.

There are a few explanations for why the data doesn’t align with what Dipoto was saying. In 2015, Statcast was brand new. It’s possible, though unlikely, that the data is miscalibrated. It’s also possible that during his rehab from Tommy John surgery, Rumbelow changed the characteristics of his pitches. Whether it was a conscious effort to generate more spin or a result of different mechanics to avoid reinjury, we just don’t know.

I was still intrigued though. The mystery of Rumbelow’s pitches was baffling, gnawing at the back of my brain. So I went back to the available data we have and tried to come up with a way to extrapolate what could be expected from Rumbelow’s pitches. I’ve often used pitch comparisons to show how a pitch from one pitcher could be as effective as a pitch from another pitcher with similar raw characteristics. We have that data from his brief time in the majors two years ago, pulled from Brooks Baseball. Let’s see who he resembles.

Fastball

Rumbelow throws a straight fastball with a bunch of “rise” on it. As Dipoto explained on the podcast, and as we know from physics, a “rising” fastball is a high-spin fastball that stays at the apex of its trajectory longer, making it appear like it’s rising. One of the reasons why I thought the Statcast data from 2015 was miscalibrated was because of the abnormally low spin rate for Rumbelow’s fastball. We can see that he generates a significant amount of “rise” on the pitch yet the calculated spin rate doesn’t align with that kind of vertical movement.

As far as his comps go, they’re all pitchers who possess above average whiff rates on their fastballs. The average spin rate these five pitchers generate is 2266 RPMs, which almost exactly matches the league average spin rate for a four-seamer. I wouldn’t be surprised if Rumbelow’s fastball actually runs a spin rate closer to what these five comps are running.

Curveball

Rumbelow’s curveball is pretty tight without a lot of drop or horizontal movement to it. It looks pretty similar to a slider actually. The average spin rate for his comps is 2366 RPMs, well below the league average for a curveball. Unless his curveball’s characteristics changed significantly after Tommy John surgery, it’s hard to see how this pitch stands out.

One of the things Dipoto mentioned on the podcast was looking for fastball/curveball pairings that played off each other. The idea is that a curveball that looks like a fastball out of the hand is much harder to hit—and therefore generates a higher whiff rate—than a slow, looping curveball which might be more effective because of how different it is from a fastball. The average spin rates for Rumbelow’s pitch comps are relatively similar. A cursory glance at video from 2015 and 2016 shows a fastball and curveball that look similar out of the hand. Maybe this is what Dipoto was referencing when he called out Rumbelow as a Statcast darling.

In the end, we just don’t know much about Rumbelow’s pitch repertoire yet. The pitch comps for what his pitches were before his surgery point to an average “rising” fastball and a curveball that doesn’t appear remarkable. But perhaps in concert these two pitches enhance each other. Without actual data points from after his surgery, we don’t really know if his pitch characteristics have changed or not. Either way, I’m interested to see what Statcast reveals about Rumbelow once the pitches start flying during spring training. Dipoto certainly seems to think there’s something there.