How challenging is the transition between minor league levels?

To address this question, I analyzed 2024 data for professional baseball players who logged at least 50 plate appearances (PA) or faced 50 batters (TBF) at two or more levels.

For hitters, I measured the difference in wRC+ between levels. For pitchers, I used FIP-. To get a final number I applied a weighted average for each transition, based on the lower sample size between the two levels.

Results for Hitters

The table below shows the drop in wRC+ when players advanced levels, along with the corresponding sample size:

• CPX to A: -41.6 wRC+ (8,310 PA)
• A to A+: -27.4 wRC+ (17,294 PA)
• A+ to AA: -32.4 wRC+ (15,622 PA)
• AA to AAA: -26.4 wRC+ (15,588 PA)
• AAA to MLB: -37.9 wRC+ (20,700 PA)
  

Results for Pitchers

The table below shows the increase in FIP- when pitchers advanced levels, along with the corresponding sample size:

• CPX to A: 28.8 FIP- (11,079 TBF)
• A to A+: 19.3 FIP- (19,475 TBF)
• A+ to AA: 15.8 FIP- (19,720 TBF)
• AA to AAA: 20.7 FIP- (19,165 TBF)
• AAA to MLB: 24.6 FIP- (26,138 TBF)
  

Difficulty Ranking

To create a unified view, I normalized the results for both hitters and pitchers and averaged them. Here’s the ranking of level transitions, from “easiest” to “hardest,” along with how they compare to the overall average difficulty:

1. A+ to AA: 14.1% easier than average
2. A to A+: 13.7% easier than average
3. AA to AAA: 12.8% easier than average
4. AAA to MLB: 12.9% harder than average
5. CPX to A: 27.7% harder than average