Doing the same for pitchers is a trickier business. A pitcher's Breakout Rate is based on the likelihood that he'll improve his Equivalent ERA by 20 percent relative to the weighted average of his performance over the past three years. Alas, pitcher development is a less predictable enterprise than it is for hitters, who generally peak between ages 25 and 29, so there are a few problems in identifying true breakout candidates among pitchers.
The primary difficulty is that the up-and-down nature of most pitching careers means that pitchers of any age might post high Breakout Rates, particularly when their recent performance includes injury-related ineffectiveness. Among the small handful of pitchers with at least a 30 percent rate are veterans Randy Johnson, A.J. Burnett, Jeremy Bonderman and Ervin Santana, and that's after weeding out the small workloads (either due to injury-related attrition or to relief roles) and Ugueto Effect equivalents. Even after eliminating the noise, the Breakout Rates among our meaningful set of hurlers wind up being about half those shown by the hitters.