When a prospect moves up a level it seems to always be considered the "biggest jump" within the minors – at least at that moment in time.
What is the biggest jump for a minor league player and why?
Denis Savage, MadFriars.com:
In rookie ball you often see the flamethrowers that don’t have control. It is a scary place to be. That is nothing, in comparison, to what prospects face in Double-A and why the jump from High-A to Double-A is so huge.
The talent on the mound intensifies to a point where those wild and erratic pitchers have found control and can pinpoint their 94-MPH heat on the corners. By contrast, the hitters are no longer arbitrarily chasing sliders outside of the zone. Batters adjust on the fly. The mental game between pitcher and batter becomes just as important as the pitches and swings. While you can get away with throwing a two-strike changeup in three straight at bats at the lower levels, a hitter will crush that pitch in Double-A or lay off it when it drops into the dirt.
Most players who make it to Double-A and have some semblance of success have a real shot at reaching the majors. The raw talent is refined compared to its High-A counterpart. Success at the lower levels, however, does not guarantee prosperity in Double-A. Oftentimes, the fortune comes against players who may never make it out of High-A, whereas the talent at Double-A increases and includes only those prospects who merit advancement.
Bobby Vangelatos, InsidetheDome.com:
For me, the jump between High-A to Double-A is by far the hardest jump for a player to make in the minor leagues. The talent levels between players in Double-A and players in Triple-A are not that far off. The talent change from High-A to Double-A, however, is drastic. You can simply get away with a lot more in High-A. If a pitcher throws a bad pitch, the opposing batter might simply foul it off, or even miss it completely. A lot of hitters at the High-A level will simply look for one single pitch, and if they don’t get it, they have no shot of getting a hit.
Pitchers will often claim Double-A is the toughest level for them because they notice the talent change in batters is drastic. They are now able to make adjustments to the pitcher in the very same at bat, while in High-A and below it could take a few innings, or even games, for batters to notice what the pitcher is doing.
Batters will also note pitchers throw harder and locate their pitches better in Double-A. Your typical soft-tosser, who was able to get by in High-A and below, might not succeed at the next level because hitters are stronger.
Clubs have routinely promoted their players from Double-A straight to the majors because they realize if a player proves he can handle Double-A it’s likely he will be able to handle Triple-A. You will have older players with more experience at Triple-A, but when it comes down to pure talent – the levels are nearly the same.
Chuck Murr, Indians Ink:
The biggest adjustment is Latin players coming from the Dominican Summer League or Venezuela into American pro ball at the short-season or low Class-A levels. Not only do these players have to adjust to a significantly higher talent level, they must also make complete cultural changes, learn a new language, customs, eating, and living habits. Many are homesick and confused about their new way of life - before even having to face some college-experienced left-hander with a sharp slider who received millions of dollars to sign as opposed to their paltry low-minors paycheck.
The Cleveland organization tries to help them adapt by putting together a school during instructional league or spring training play where these players not only work on their baseball skills, but also learn English and are taught proper nutrition and living habits.
Players also going from a short-season to full-season league sometimes experience difficulty adjusting to the "grind" of a 130+ game season. These players include draft picks out of high school or college who are amazed at the lengthy bus trips and 100-game increase to their season.
Nothing, however, compares to the adjustment a player coming from another country has to overcome.
Kevin J. Cunningham, SFDugout.com:
The biggest jump I see for most prospects is from High-A to Double-A. Because of the nature of the Single-A levels, you often find more ‘filler’ at the lower levels.
In Double-A, roster space is tighter, resulting is deeper lineups and rotations, and less chance of players padding their stats and performance, or coasting through weaker spots in the lineup.
With more consistent pressure to perform and being so close to the majors, I most often see Double-A as the level where hot performers from High-A cool off.
Tot Holmes, LADugout.com:
It seems to me the biggest jump is from Double-A to Triple-A. A great many prospects move up the ladder without a hitch until they run into the "just about to make the show" level and "just coming down from the show" players who are only a tick below major league quality.
If the prospect has any weakness, this is the level it is exposed, and, if he can't correct it, he'll be a minor league lifer or headed back to “real life”.