When a prospect is at the lower rungs of the minor league ladder, the value of their statistics can be mixed. The quality of play is both variable and a long way from the majors in quality. Go back five years and look at any low-level minor league's leaderboard and you'll find a few real major leaguers today mixed with a whole bunch of guys who never even reached baseball's highest level of play.
Now, look at a Triple-A league and you see a lot more value to the statistics. For example, of the top 25 players by OPS in the 2012 Pacific Coast League, 24 of the 25 made the majors -- Brian Cavazos-Galvez the lone exception -- and you see a number of players who became stars at the major league level, most notably Anthony Rizzo, Josh Donaldson, Eric Thames, Jedd Gyorko, Wil Myers and Adam Eaton.
Projection systems reflect this uncertainty, and you'll rarely get one like the ZiPS projection system to display any irrational exuberance about a player down in the Sally (South Atlantic) League. If you look back at the ZiPS Top 100 prospect list from before the season, you'll see more players in the upper minors than on the lists of the prospect mavens, such as Keith Law.
But ZiPS is designed to know when it's wrong, and when a player does succeed in the high minors, ZiPS will generally react fairly quickly. It would be a mistake to look at a projection as a number etched in stone, but merely a snapshot in time, taken at a particular point in a player's career.
Below are some of the largest breakout 2017s in ZiPS among minor league hitters, the players with the 2017 seasons that most moved the needle on the projections. We list each player his respective parent organization.
Jake Cave, New York Yankees
Preseason projected OPS: .617
Current projected OPS: .709
Projected increase: 92 points
Of the 1,400 projections for hitters run by ZiPS coming into 2017 (about 1,250 "official" ones and 150 for prospects at very low levels for which I have little confidence), only four players got a larger boost than Cave's 92-point OPS boost: Ryan Zimmerman, Aaron Judge, Justin Smoak and Zack Cozart.