While I don’t believe that ground ball rates are the most important, or even among the few more important things that a pitcher can control, they do help. While ground balls go for hits more often than fly balls, they go for extra-base hits less often, result in more double plays and none of them ever go over the fence for a home run.
Pure ground ball rates for minor leaguers are tough to come by. The official website for Minor League Baseball doesn’t list them. Fangraphs doesn’t have them. Baseball-Reference doesn’t have them. Lesser known First Inning has them, but their numbers aren’t always complete and they haven’t updated their SQL queries to reflect the AZL Reds, so they don’t have any rookie level players rates. Ground ball rates, rather than ground out/fly out, actually can tell us the true effectiveness. GO/FO only tells what happens when a ball is turned into an out. Fly balls are turned into outs about 33% more often than ground balls are, so that stat is missing out on a lot of data. Below, I looked at the pitchers that I included in my Reds Top 40 Prospects from the 2013 Prospect Guide. I sorted them from highest ground ball rate, to lowest ground ball rate. I also included the number of innings that the pitcher threw. Guys without many innings thrown aren’t likely to have their rates be all that reliable. The more innings, they more reliable their numbers become.
The average Major Leaguer over the past few years has had an average ground ball rate in the 44-46% range. You can obviously succeed being lower than that (Justin Verlander was at 42% last year) and you can be a below-average pitcher despite being above-average at inducing ground balls too (Chris Volstad was at 49% last year and posted an ERA of 6.31). Studies have shown that generally, as a pitcher advances up the ladder, their ground ball rate lowers by 1% at each level. That doesn’t apply to everyone and there are different reasons for changes (changes in mechanics, improved velocity, improved breaking ball, picking up a cutter/2-seamer, improved control allowing you to pound the bottom of the zone or any other reason you could think of), but is a general guideline to follow.
Anyone who finds themselves in the 50% or higher range is among the better ground ball pitchers in any given league. When a pitcher gets below that 40% range, they are among the worst ground ball pitchers in any given league.
Kyle Lotzkar is on the extreme low end, especially given how many innings he threw and his history of being an extreme fly ball pitcher. Nick Travieso is at the same rate, but he also had a grand total of 66 balls put in play against him. On the flip side, Amir Garrett posted an incredible 59% ground ball rate. However he, like Travieso, had a very limited number of balls put in play against him. Curtis Partch, Chad Rogers and Drew Hayes all being at that 50% threshold with a significant number of innings is impressive.