Ride or Die: Fastballs Running on IVB?

Induced vertical break (IVB) is a measure of how much vertical movement or ride a fastball has. It can be an important factor in determining the shape of a pitcher’s fastball, and some pitchers are much more reliant on it than others. It can be the difference between six to seven innings and getting pulled after four and a third. As we get to the final weeks of the season, movement and ride on a pitcher’s fastball can begin to degrade after the wear and tear of the season. This piece will look at what kind of pitchers are reliant on IVB for success, which pitchers have been most impacted by the wear and tear of the season, and who is still able to maintain vertical movement in the final stages of the season. Which pitchers’ four-seams actually depend on IVB, and where is that IVB heading right now?

Across over 200 starters from this season, of course, the relationship between each pitcher and IVB will be quite different. Tracking something like IVB to see the relationship with things like whiff and run value is difficult to do. IVB can vary greatly start to start, and the results can also be susceptible to noisy outcomes on the day.

For each qualified starter (20% or higher four-seam usage, at least 10 starts), every start this season is one observation: that start’s average four-seam IVB paired with that start’s four-seam run value (RV) and that start’s four-seam called+swinging strike% (CSW), with the correlation computed across all of a pitcher’s starts. RV captures everything, including contact quality, and CSW captures swing-and-miss and called strikes.

The correlation score runs from −1 to +1.

For run value, a larger negative score means IVB correlated to better results (lower run value is better for the pitcher), so a pitcher at −0.50 sees his fastball perform noticeably better in starts where his ride is up, while one near zero IVB has no relation to the RV of his four-seamer at all. For CSW, a higher positive score, closer to 1 means more IVB led to more called strikes and whiffs.

Basically, a higher number indicates reliance on IVB for bat missing (positive), or overall effectiveness (negative). A pitcher strong on both, like Shohei Ohtani (−0.41 RV, +0.44 CSW), gets more swings-and-misses and gives up less damage when his ride is up, so he relies heavily on IVB for his fastball to be successful. One strong on RV but not CSW, like Kyle Harrison: −0.41 RV, −0.09 CSW, gets his value from weak contact, not whiffs.

IVB can also move with or independently of velocity. Drew Rasmussen‘s IVB gained nearly two inches with velo going the other way (r = −0.33). George Kirby’s IVB gained with velo flat (r = −0.05). These are movement gains, not arm-speed spikes. Contrast with Zebby Matthews (r = +0.38), where IVB and velo move together.

The table below lists the 20 starters whose four-seam results are most closely tied to their IVB on a start-by-start basis this season.

• The IVB→RV column measures how strongly a pitcher’s ride correlates with his fastball run value in a given start, with a more negative number meaning better results when the ride is up.
• IVB→CSW measures the same relationship against called strikes and whiffs. A positive number signifies CSW is up.
• IVB→Velo shows whether the ride is moving with velocity or independently of it, where a number near zero means the IVB is shifting on its own, not just because the arm is throwing harder or softer.

Tracking the IVB of starters, I took a season-long view, comparing the average from the first five starts of the season against the most recent five starts. That change is the vertical axis on the chart above, showing who has gained or lost ride across the full year. The horizontal axis pairs it with how tightly each pitcher’s IVB correlates with his fastball run value, so a pitcher sitting in the top right has both gained IVB and relies on it for results. From the initial pool of 205 qualified starters, I ranked by run value correlation to narrow to 20 pitchers whose fastball results are most tightly coupled to their ride. I chose to rank through run value rather than building a composite score or off of CSW because a composite would shift the focus toward pure swing-and-miss arms.

This would exclude pitchers like Harrison, whose IVB works through weak contact rather than whiffs, giving us a more diverse pool of pitchers to look at.

As we look to the top right of the chart, we get pitchers who are not only reliant on IVB but have been able to actually improve the vertical movement on their fastball as we move to the latter stages of the season. George Kirby is an example of a pitcher whose ceiling is really unlocked by increased IVB on his four-seamer, as he has been able to keep raising this ceiling as the season has gone on. Despite an inconsistent season, his most recent performance was his best outing, where he went into the eighth inning. Kirby’s four-seam averaged 15 inches of induced vertical break, a full inch above his season average, and hitters swung through it at a 50% clip (12 whiffs on 24 swings) with a 46% CSW rate on the pitch. This was maintained well into the eighth inning, where he was still able to beat bats at the top of the zone at high velocity; not only has he increased from the start of the season but has also steadily risen since the break.

Chris Sale and Drew Rasmussen are two very encouraging examples of pitchers maintaining vertical movement despite suffering long-term injuries and aging. Rasmussen, pitching his first full season without any load management since going under multiple elbow surgeries, has added nearly two inches of ride on his four-seam across the 2026 season, from 16.8 in his first five starts to 18.8 in his most recent five, and he’s done it without throwing any harder or adding any further strain to his elbow.

Sale, now 37 and 24 starts into his season, has gained just under an inch of IVB across the year while his velocity has held steady in the mid-90s. His IVB has settled around 10.3 to 10.4 inches in his most recent outings, above his season average of 9.8. Sale also featured in my increased velocity piece, so it is not surprising he has also added vertical movement, but incredibly impressive nonetheless, as he threw a complete game against the Dodgers, constantly challenging the top of the zone.

But as we can see from the chart, some pitchers are not so lucky, and they are not only reliant on IVB for their fastball to be successful, but the vertical movement is also in decline.

Tanner Bibee is experiencing the sharpest regression in IVB of any pitcher in 2026. His four-seam has shed over two inches of ride across the season, from 15.8 in his first five starts to 13.7 in his most recent five, and his last outing cratered to 11.0. While he does also throw his sinker around 20%, which has graded out better than his four-seam, he primarily relies on his cutter, which in velocity and shape profiles much closer to a traditional slider with more vertical movement than a fastball.

Braxton Ashcraft’s numbers tell a subtler story. His season-long IVB drop is small, just a quarter of an inch over the season, but has had a fair bit of fluctuation, as you can see below.

But he carries the strongest IVB-to-run-value link on the entire list at −0.58. That coupling means even modest movement matters more for him than a two-inch swing does for a pitcher near zero, and the contact rate on his fastball has increased every month as the season has gone on. So while the IVB is not degrading as much as most, it is much more sensitive to any drop in vertical movement.

Finally, it is difficult to ignore one Shohei Ohtani in this group, as he gears up to start pitching again. He is heavily reliant on IVB for both low run value and swing and miss. However, given he has not pitched since July, it is not possible to get a read on if his IVB is holding up, but it will be worth paying close attention to when he does return to the mound.