John Brebbia, Edgertronics, and what happens when you get under a slider



At the start of spring training, John Brebbia was spotted using an Edgertronic and sensor to analyze his spin rate, spin axis, and pitch velocity. Edgertronics are beyond my expertise, but the video they produce looks amazing. In baseball, they’re typically used for pitch design and refinement. What makes a pitch good, and what could make it better?


Given the opportunity with John Brebbia, I’d start by taking a look at his slider. Brebbia’s slider has been his best pitch so far in his career, at least according to FanGraphs run values. In 2017, it was +5.4 runs above average and a top 40 slider among relievers. It took a step back toward average the next year, but returned to form in 2019. In fact, at +11.1 runs, it was just as good as Adam Ottavino’s frisbee and ranked as a top ten slider among all relievers. Here’s a snapshot covering most of the results that matter:

By total run value and run value per 100 sliders thrown, John Brebbia’s was among the best sliders thrown in 2019. He threw it for a ton of called strikes and it was in the 80+ percentile for wOBA and xwOBA. It didn’t generate many whiffs and it was rarely hit on the ground, but overall the pitch did its job nicely.


Despite how well the pitch performed last year, though, it’s fair to wonder if this is a sustainable profile. The best sliders get whiffs. Called strike rate doesn’t appear to stick quite as well as whiff rate, and to get called strikes you have to throw in the strike zone. The league average wOBA against all sliders in the strike zone last year was .327, which was slightly better than the overall league average. That rate jumps to .348 when hitters swung. It stands to reason that, if you don’t have a whiff-worthy slider, hitters might start swinging more often when you throw it in the zone. Sliders in the zone are better than fastballs in the zone, but pitchers still don't want to throw them there when hitters are swinging.


I mentioned in an article earlier this week that John Brebbia’s peripherals in the second half of last season began to deteriorate, and I speculated that his slider was the likely cause. After that published, I pulled his slider data. In the second half of last season, the pitch’s movement profile shifted:

Sliders thrown through June 30th are represented by blue squares and those thrown in the second half are red circles. There’s overlap in the middle, but there’s a lot more red in the top left and a lot more blue in the bottom right. The shape of the pitch was a little different in the first half than it was in the second half. It’s subtle in the aggregate pitch data, but the difference is there:

Velocity declined a little and spin rate dropped with it, but neither of those measures changed enough to say anything was meaningfully different. Horizontal break basically stayed the same. The vertical movement reading from Pitch f/x shows that Brebbia's slider actually gained a little rise and, as a result, the total vertical break decreased despite a slight velocity decline.


So why did the pitch drop less (or rise more)? Here’s the same table, but this time with spin axis included:

There! Spin axis is reported on a 360-degree scale with 180 degrees representing backspin, and 90/270 representing sidespin. By increasing his spin axis from ~115 to ~125, Brebbia put more backspin on his slider relative to the amount of sidespin. With spin axis measurements, there’s a lot of pitch-to-pitch variance but it doesn’t look like change this was an accident. Prior to July, Brebbia had never averaged a spin axis higher than 120 degrees in any month. Then, beginning in July, Brebbia’s release point when throwing his slider suddenly got higher. Afterwards, from July through October, he averaged higher than 120 degrees in every month. Put simply, Brebbia’s average second half slider had more backspin than his average first half slider. How might that look in action?

Thank goodness for Andrew Perpetua (who is probably squirming at how I’m using his incredible tool and not-physics) and for the overlay and edits by @cardinalsgifs.


The green ball is thrown on a ~115 degree axis at 84.0 miles per hour and ~40% spin efficiency (in line with Brebbia’s Active Spin Rate). The orange ball is thrown at ~125 at the exact same speed in the same starting location. The orange ball drops less, because it has more backspin. It breaks less horizontally, because it has less sidespin. Closer up, enhanced and re-oriented by @cardinalsgifs, the difference looks like this:

What happens when a slider slides less? That inch can sometimes be the difference between a line drive and a grounder or between contact and a whiff. Check out this one against the Nationals in the NLCS:

That was in an 0-2 count. Out of the hand, Brebbia probably felt pretty good. He got under it, though - a spin axis of 153 degrees indicates this ball had more backspin than sidespin. The vertical movement due to spin (ignoring gravity effects) was +2.7 of rise. Obviously, this ball broke downward, but it dropped about 1-2 inches less than Brebbia was used to. Instead of ducking down and away from the batter, this slider's backspin held it where Zimmerman could handle it. He didn't miss. The guy on second scored, and Zimmerman replaced him at second base.


When John Brebbia started getting under his slider, a good slider got less good. Here’s the same pitch value chart that we started with, but now broken out between the season’s first half and second half:

From Brebbia’s perspective, his xwOBA and ground ball rates were very slightly better in the second half, but not meaningfully (the difference in ground ball rate was literally one grounder). wOBA against the slider was up slightly, and run value dropped, as did the called strike, whiff, and whiffs per swing rates. Performance didn’t totally deteriorate, but the supports were less sturdy.


Then there’s that wOBA. A .227 xwOBA is really good, and it lines up exactly with the expected results. Most of us, myself included, have been conditioned to take that as a definitely-good thing indicating that Brebbia earned his results. Earned results are more likely to re-occur than lucky results.


What you don’t see here, however, is that Brebbia’s wOBA and xwOBA were suppressed by one of the highest popup rates in the majors. The ability to induce pop-ups doesn’t appear to be a repeatable skill. So, Brebbia didn’t get lucky on the balls that were hit, but he was lucky on the types of balls that were hit. On other types of batted balls, he managed a better than average wOBA on contact in 2019 but didn’t in 2018. Chances are that if he doesn’t get more whiffs and grounders, hitters will start to do more damage. To get more whiffs and grounders, he might need a better slider. Good thing the Cardinals finally got that Edgertronic.

As always, big thank you to @cardinalsgifs for his work on this piece, and to Baseball Savant, FanGraphs, and Brooks Baseball for all the data used in the post. Special shoutout to Andrew Perpetua for his incredible efforts. Play with his site.