Centerfield wrote: I guess the part that confused me was his claim that exit velocity settles in after 50 balls in play. well, that's statistics. Calculating exit velocity as you go along during the season, right around 50 balls in play is where the values pretty much exactly resemble the overall season averages. But that's only for in-season values. We don't know how 2017 velocities predict 2018 ones, especially inregards to aging. So yes, a 21 year old is expected to age and mature. initial research seems to suggest that the floor/average values tend to increase at first, but the peak only comes down. Of course there's a somewhat limited sample of pre-fully developed players that have enough data to really figure this out for sure. I'd guess the idea is that if you're a major league player, you'll occasionally catch up to the flat fastball and hit it as hard as you can, at some point, during a season. You're not going to square it up better with more practice, you pretty much did it perfectly, so your aging dying body will only decrease, unless perhaps Rosario is still on the upswing portion of growth and aging and then maybe he can tweak some more out of it? man, I'd love to have some Bonds exit velocities.