Advancement in one's profession brings with it uncertainty. Minor league players are no different than the 9-to-5 professional in this regard.
Players promoted to a higher level of the minors must find new living arrangements in their new home city. They must integrate into the framework of a new clubhouse and adapt to the style of a new manager.
Oh, and they must maintain their level of production against the best competition they've ever faced.
But a few aspects of player advancement in the minors are more certain than others. In fact, three statistical rates move in a linear fashion as players move up the ladder from Rookie ball to the major leagues.
1. Home runs increase
2. Stolen-base attempts decrease
3. Errors decrease
These trends were universally true in 2016 as players advanced from the Rookie-level Arizona and Gulf Coast leagues to the American and National leagues.* These trends also existed when I sampled 2006 and 1996 data.
Here are the trends in chart form, where PA stands for plate appearances and TC for total chances:
One can view these rates for home runs, stolen bases attempted and errors as the Three Absolute Truths Of Player Development because of their inevitable progression. Additionally, the same linear progressions exist in rates ancillary to the ones cited, such as extra bases, stolen bases and measures for physical errors such as hit-by-pitches, wild pitches and passed balls.
What these player-development trends might mean for organizations is that as players advance in the minors—no matter the leagues in question—they keep moving to contexts where defenses are tighter, opposing batteries are better at holding baserunners and the players around them are hitting more home runs. This is universally true, whereas rates for things like walks, strikeouts, singles, doubles and triples bounce around from level to level.
Then factor in the historically high strikeout rate and historically low singles rate in the majors today, and these trends taken together would conspire to push players and teams toward a "quick-strike" mentality that prioritizes home runs.
No one disputed this point, but front-office executives I contacted did raise a number of other interpretations of the data.
Players are not randomly assigned to minor league affiliates. They typically earn their promotions (or demotions) because they have demonstrated skills that warrant a higher or lower level of play.
For instance, better hitters tend to hit the ball harder (more home runs), pitchers tend to improve their times to the plate—or else move to the bullpen (fewer stolen bases)—and teams tend to move overtaxed defenders to easier positions (fewer errors).
Well, Player Development
Scouts have long observed the axioms that power increases as players grow older and stronger, just as speed decreases. This natural biological development is partially responsible for the trends observed in the rates for home runs and stolen bases attempted. Performance data for domestic minor league players last year, sorted by season age:
Furthermore, players are encouraged early in their pro careers to be aggressive in an effort to learn how to develop their skills. For instance, players at the lower levels of the minors are encouraged to run more often (more stolen-base attempts), play more demanding defensive positions (more errors) and execute various small-ball techniques, such as bunting or the hit-and-run to gauge aptitude (fewer home runs).
Value Of Athleticism
As players advance in pro ball, speed becomes more important to run-prevention than run-creation. In other words, fast players who ran at will against low-level minor league pitchers and catchers see those stolen-base attempts diminish against more advanced batteries. However, those advantages in terms of speed and athleticism tend to manifest on defense, where faster, rangier players tend to be stronger defenders who commit fewer errors.
* The Rookie-advanced Appalachian and Pioneer leagues are omitted because they tend to be hybrids between the AZL and GCL complex leagues and the short-season New York-Penn and Northwest leagues.