@Consultant Bob, I thought about your question a lot. I think it is a combination of:
- The 10,000 hour rule. Some if it just getting good quality repetitions. The more you play, the easier it is to anticipate a bounce, get a better jump, make a difficult play look routine. Because you've done it before. Long season is over 130 games. It's hard not to get better with that much baseball.
- Raw natural talent. The higher you go up, the more likely it is that you are dealing with athletes with better natural tools. Some guys are just different.
- Hard Work. When the boys started talking about video games, Justin said he didn't have time for it because of his conditioning schedule. Yoga, pilates, lifting, infield work, batting cages. How hard do you push yourself in practice, in the off season, how serious do you take your lifting, your agility drills, etc.
- Knowledge. There is so much information available to players now, especially as you get into higher levels of college and pro baseball. Whether a guy is a pull-side hitter, average exit velos, tendencies against certain pitches. A true student of the game can give himself an edge on defense if he utilizes the information available (coaching plays a role in this as well). It is also interesting at the pro level how much the information available varies from team to team.
I think the relative weight of each of these 4 factors really depends on the athlete. Someone with less natural ability may depend more on 3 and 4. Someone with a real thirst for the game may be able to overcome deficiencies in 2, etc.
P