Not every top prospect hits the ground running the way recent Rookie of the Year winners like Evan Longoria and Ryan Braun did, stepping into a major league lineup and putting up All-Star caliber numbers. Sometimes it takes a couple of years' worth of experience and adjustments for a high-upside player to reach his potential, but when he does, look out.
Our PECOTA projection system can help to identify such players via a trio of categories called "breakout," "improve" and "decline," which estimate the likelihood of a player's production significantly rising or falling relative to his established baseline level. "Breakout rate" is the percent chance that a hitter's equivalent runs produced per plate appearance will improve by at least 20 percent relative to the weighted average of his performance over the past three years. A high rate generally indicates a high upside, though it's worth noting the Ugueto Effect, in which the system will estimate a high rate for a horrible player simply because there's nowhere else for him to go.