I studied the minor league K-rates of successful young big league pitchers the past season, and found that most of them had K-rates over 20% in the minors. That led me to post an article arguing the importance of K% in the summer. However, what I did not do was post the results of those successful big leaguers. Now, I'll take another look at this analysis, and expand the number of pitchers and list the results here in this article. I generally assume the age of 23 or lower to be age appropriate for AAA, with each level below that one year lower. So 22 for AA, 21 for A+ etc. I'm using a minimum of 50 IP for each level.
Of course, which pitchers can be described as successful big leaguers is a bit subjective, but I think the list contains few pitchers that wouldn't be welcome on most, if not all major league rotations. If I omitted or included pitchers you disagree with, please bring it up in the comments.
Rookies in 2006
Jered Weaver - A+/AA (22): 29.4%, AAA (23): 31.5%
Matt Cain - A (18): 29.7%, A+/AA (19): 24.5%, AAA (20): 28.1%
Francisco Liriano - Rk- (17): 28.1%, A (18): 25.8%, A+ (20): 26.1%, AA/AAA (21): 30.9%
Justin Verlander - A+/AA (22): 30.0%
Cole Hamels - A/A+ (19): 38.4%
Josh Johnson - A (19): 16.9%, A+ (20): 20.6%, AA (21): 18.9%
James Shields - A (19): 21.4%, A+ (21): 18.8%, A+ (22): 18.5%, AA (23): 23.8%
Anibal Sanchez - A- (20): 32.6%, A+/AA (21): 28.4%, AA (22): 25.1%
Jon Lester - A (19): 15.7%, A+ (20): 25.4%, AA (21): 27.1%
Adam Wainwright - Rk-/Rk (18): 34.5%, A (19): 26.6%, A+ (20): 23.9%, AA (21): 21.4%, AAA (22): 22.7%
Matt Garza - A (21): 27.2%, A+/AA/AAA (22): 29.0%, AAA (23): 23.7%
Chad Billingsley - Rk (18): 27.6%, A+/AA (19): 28.5%, AA (20): 26.9%, AAA (21): 26.3%
Jonathan Sanchez - A (22): 31.1%, AA/AAA (23): 34.7%
Shaun Marcum - A/A+ (22): 25.8%, AA/AAA (23): 19.4%
C.J. Wilson - Rk/A (20): 26.7%, A+ (21): 16.3%, AA (22): 16.5%
Edinson Volquez - A/A+ (20): 20.4%, A+/AA (21): 24.2%, AAA (22): 25.5%
Rookies in 2007
Yovani Gallardo - A (19): 21.9%, A+/AA (20): 30.8%, AAA (21): 34.9%
Ubaldo Jimenez - Rk (18): 22.6%, A (19): 21.4%, A+/AA (21): 22.3%, AA/AAA (22): 23.1%
Dallas Braden - A+/AA (21): 23.2%, AA/AAA (23): 28.5%, AAA (24): 25.6%
John Danks - A/A+ (19): 25.1%, A+/AA (20): 20.5%, AA (21): 25.2%
John Lannan - A- (20): 13.9%, A (21): 18.6%, A+/AA/AAA (22): 15.0%
Rookies in 2008
Jair Jurrjens - Rk-/A- (18): 21.0%, A (19): 18.4%, A+/AA (20): 19.9%, AA (21): 20.0%
Clayton Kershaw - A (19): 32.4%, AA (20): 24.5%
Johnny Cueto - A/A+ (20): 26.1%, A+/AA (21): 25.3%
Max Scherzer - AA (22): 23.8%, AAA (23): 36.1%
Jordan Zimmermann - A- (21): 32.9%, AA (22): 23.5%
Clay Buchholz - A (21): 28.5%, AA/AAA (22): 34.5%
Ian Kennedy - A+/AA/AAA (22): 29.1%, AAA (23): 25.7%
Gio Gonzalez - Rk/A (18): 24.9%, A/A+ (19): 30.9%, AA (20): 24.3%, AA (21): 30.3%, AAA (22): 24.4%
Jaime Garcia - A/A+ (19): 20.6%, AA (20): 22.0%, AA/AAA (21): 21.0%
Jonathon Niese - A (19): 24.0%, A+ (20): 19.1%, AA (21): 21.5%, AAA (22): 20.5%
Rookies in 2009
Brett Anderson - A/A+ (19): 25.0%, A+/AA (20): 27.1%
Ricky Romero - A+/AA (21): 19.5%, AA (22): 19.6%, AA/AAA (23): 16.0%
Jeff Niemann - AA (23): 26.3%, AAA (24): 21.3%, AAA (25): 23.4%
Tommy Hanson - Rk (19): 26.9%, A/A+ (20): 27.7%, A+/AA (21): 29.2%, AAA (22): 35.0%
David Price - A+/AA/AAA (22): 24.8%
Trevor Cahill - A (19): 26.8%, A+/AA (20): 27.5%
Doug Fister - AA (23): 15.2%, AA (24): 17.3%, AAA (25): 17.3%
Mat Latos - A- (19): 30.1%, Rk-/A-/A (20): 29.7%, A/AA (21): 27.3%
Jhoulys Chacin - Rk (19): 20.3%, A/A+ (20): 22.5%, AA (21): 20.0%
Madison Bumgarner - A (18): 29.9%, AA (19): 16.4%, AAA (20): 17.0%
Analysis
My 20% rule seems to work well, at least for groundballers. Flyball pitchers who are successful in the majors seems to be above 24% most of the time. Also, college draftees seem to post more obscene strikeout-rates than high school draftees. There are, of course, a few exceptional cases. Out of the 41 pitchers listed, 10 had seasons below 20% Ks. However, only 3 never topped 20 in their minor league careers, suggesting that any pitcher who never dominates like that is awfully unlikely to ever become a solid starting pitcher.
Looking at the guys who succeeded despite not getting to 20%, I'll start with Ricky Romero. Ricky is a groundball pitcher who didn't actually get a good percentage of groundballs until his last minor league season, where he did top the 20% Ks-plateau in AAA (only 14.4% in AA that season). He's a successful case of making adjustments to huge effect. Doug Fister is a late bloomer who no-one saw coming, and who recently added a significant chunk of velocity to remain successful (now that SAFECO won't protect him any longer), whereas John Lannan has added as much as 3 mph to his fastball since he came up to the big leagues, but we still don't know if he's actually good or just lucky.
The same question, good or lucky?, can be applied to Jair Jurrjens, who was, in fairness, always close to or above 20% Ks. Josh Johnson added a lot of velocity late, while C.J. Wilson added velocity later as well, and then moved from the pen to starting successfully. James Shields, well I don't know why his pitching skills didn't translate into more strikeouts, but it should be noted that his best season for strikeouts was his last in the minors. Madison Bumgarner was really young (3 years younger than 'standard') for his level when he K'd so few, and he had velocity issues at the time. Marcum and Niese were never far below 20, while Lester quickly and drastically improved after a lacklustre first season.
Conclusion
I'd like to conclude this article by stating that I think minor league pitching stats, specifically the K-rates, are underrated as a tool of evaluation. People, especially Jays fans, often use anecdotal evidence that pitchers can improve by pointing to a guy like Halladay, or Romero, to argue that we shouldn't take minor league stats too seriously. Well, perhaps we should, because the case of Romero is very rare. Depending on what you think of Fister, #1-2 starters just don't produce low K-numbers in the minors. If a guy who is pegged as future top of the rotation starter is not getting Ks, something's wrong. And the odds are always against someone who has to make drastic improvements, like Drabek, Wojciechowski, and Jenkins. Henderson Alvarez (18.7% Ks in AA) might make a lot of you optimistic about the chances of other low-K guys, but even if he does succeed for an extended period in the MLB (and we're all hoping he does), that won't change the fact that it's just very hard to not K a lot of people in the minors if you have MLB-worthy "stuff".
Taken together with John Sickels' recent statement that he now thinks pitching prospects are easier to predict than hitting prospects, despite the high frequency of injuries, we should throw away the old "there is no such thing as a pitching prospect" line. Because there clearly is, even if there might not be such a thing as a "sure thing pitching prospect". With all the pitching prospects AA has added to the Jays' system in recent drafts, watching the K totals from our pitching prospects will be a fun occupation over the next few years.