The term "upside" is used across sports as a way to describe a ballplayer's potential if he developed in a perfect world, one in which all of his skills were polished and his physical abilities were free to reign supreme. The idea of "upside" requires us to assume that technical proficiencies -- such as strike zone awareness, breaking ball recognition and fastball command -- are all learnable or teachable, while physical attributes such as arm strength, speed and power mostly are not. A prospect described as "high upside" in baseball has those physical attributes, and it is hoped that, if he lacks polish, feel, instincts or other baseball abilities, those will come with time and repetition.
Evaluating athletes based solely on upside can be dubious. Many athletes across sports excel due to technical proficiency more than raw physical ability. This is especially evident in baseball. Beer-drinking, chicken-eating Wade Boggs was much more effective than Bo Jackson, and Jamie Moyer evolved and survived on nothing but pitchability toward the end of his 25 years in the big leagues, while legendary flamethrower Steve Dalkowski never got there.
But statistical leaderboards are full of prototypical athletes with prototypical bodies and loud tools. Here are this year's examples of minor leaguers who possess the most superlative of these physical attributes at the plate, discussed here without concern for statistical performance, proximity to the majors or anything but their assumed upside. To make this list, a prospect can't be in the big leagues yet (so no Yoan Moncada here).
10. Bubba Thompson, OF, Texas Rangers: Thompson quarterbacked McGill-Toolen Catholic High School to Alabama's 7A state championship game. He was a multisport commit to Alabama but was drafted 26th overall by Texas and chose baseball. He began making more authoritative contact as a senior and has shown flashes of power in pro ball, and he's likely to grow into more power as his lean, 6-foot-2 frame fills out. He's still getting comfortable against pro pitching but seems to track pitches well while showing some feel for opposite-field contact. He's a long-term project, but his plus-plus speed and improving power are very exciting.