Strikeout Rate for AFL Pitchers as Indicator of Future Success

The Arizona Fall League is a remarkable spectacle for those with even a passing interest in prospects, insofar as it provides an opportunity to see many of the best ones of those (i.e. the best prospects). This year’s edition of the AFL, for example, has featured Byron Buxton, Addison Russell, and Francisco Lindor — ranked first, fifth, and sixth, respectively, among Baseball America’s midseason top-50 list. Except for the Futures Game, there’s rarely an occasion upon which one is able to witness such a substantial collection of minor-league talent.

One finds, however, that while the AFL is generally acknowledged as an excellent medium for scouting such players, that the actual performances produced by those players are largely dismissed. Even the author himself — a person with an unhealthy interest in the numbers produced in the more obscure leagues — announces something to this effect when publishing the weekly statistical reports for the AFL which appear in these electronic pages.

There’s some logic to this, of course. First, the level of competition isn’t standardized. Some participants have already made their major-league debuts; others, like 20-year-old Mets right-hander Robert Whalen, for example, haven’t even graduated to High-A baseball yet. Second, the run environment is inflated, teams averaging 4.9 runs per game thus far. In order to protect the latter group from overuse, clubs are more likely to send their top hitters than top pitchers. That, in tandem with the hot and dry weather, naturally leads to more run scoring — and slash lines and ERAs that are both higher than one is accustomed to seeing in the majors. As a result, one is accustomed to ignoring all the numbers that come out of Arizona.

Of course, given the paucity of the samples — few hitters record more than 100 plate appearances, and only a few more pitchers end up facing 100-plus batters — slash lines and ERAs would be of nominal utility even had they been produced by major-league players in regular-season play. Invaluable research by Russell Carleton reveals that such metrics as these require a season or more before they become indicative of the relevant player’s true talent.

There are, of course, metrics which become reliable in much smaller samples — most notable among them being pitcher strikeout rate, because it not only stabilizes at 70 batters faced*, but because it exerts a great deal of influence on run prevention, also. Were any single metric to forecast future success in a small sample, pitcher strikeout rate is it. Is it relevant in the context of the Arizona Fall League, however?

*As Carleton himself notes, these thresholds oughtn’t be regarded as a “magic number,” but rather “the point where a measure of reliability slowly crosses an only-somewhat-arbitrary line in the sand.”

To better understand how much pitcher strikeout rate in the AFL rate might inform future major-league success, I looked at AFL pitchers from 2005 to -09* who’d both (a) faced 70 or more batters (that is, the sample threshold at which strikeout rate becomes reliable for major-league pitchers) and also (b) made at least half their appearances as starts. Each year in the AFL there are about 25-30 pitchers who meet both those criteria. For each of the five years in question, I isolated both the top and bottom third by AFL strikeout rate, resulting in 43 “high strikeout” and 43 “low strikeout” pitchers (although it should be noted that Adam Bostick appears twice among the high-strikeout group, thus leaving the former group with just 42 different actual players).

*The earliest five-year window for which data is readily available.

The high-strikeout group produced a collective 24.9% strikeout rate in their respective AFL seasons; the low-strikeout group, a figure of just 13.2%.

Here are the 35 members of the high-strikeout group to have recorded at least one major-league appearance, sorted by RA9-WAR (that is, WAR calculated with runs allowed per inning innings, as opposed to FIP):

# Name Team G GS IP K% BB% xFIP- FIP- ERA- WAR RA9-WAR
1 Jered Weaver Angels 265 265 1688.0 20.4% 6.6% 99 93 81 31.7 41.4
2 James Shields – – – 286 285 1910.1 20.5% 5.7% 86 93 91 31.6 32.7
3 Max Scherzer – – – 207 198 1239.1 25.7% 7.6% 84 81 86 27.0 23.6
4 Ian Kennedy – – – 176 174 1066.1 21.3% 8.0% 102 99 100 13.9 14.1
5 Stephen Strasburg Nationals 109 109 649.1 28.5% 6.4% 72 75 80 15.2 13.0
6 Phil Hughes – – – 214 164 990.1 20.1% 6.2% 99 95 104 17.1 11.7
7 Tommy Hanson – – – 123 121 708.0 21.6% 8.3% 99 98 97 9.4 9.7
8 Glen Perkins Twins 339 44 559.2 18.9% 6.0% 93 93 92 7.7 7.5
9 Andrew Cashner – – – 143 51 409.2 19.5% 7.6% 95 97 89 3.8 5.3
10 Dustin McGowan Blue Jays 158 68 482.1 18.8% 9.5% 102 100 105 5.8 4.0
11 Nick Blackburn Twins 145 137 818.2 10.9% 5.7% 106 114 115 5.5 3.3
12 Brian Matusz Orioles 214 68 470.2 19.4% 8.4% 106 105 118 4.8 1.7
13 Bobby Parnell Mets 299 8 307.1 20.9% 8.7% 90 84 92 3.6 1.3
14 Angel Guzman Cubs 88 14 157.0 20.8% 10.6% 100 100 105 0.9 1.2
15 Jenrry Mejia Mets 106 18 176.0 19.7% 9.4% 99 108 106 0.5 0.9
16 Matt Palmer – – – 63 20 185.1 12.1% 11.6% 118 112 108 0.7 0.9
17 Adam Loewen Orioles 35 29 164.0 17.9% 14.2% 111 106 118 1.7 0.8
18 Charlie Morton – – – 135 134 746.2 15.6% 8.7% 105 107 117 5.4 0.7
19 Darrell Rasner – – – 41 30 165.2 12.6% 7.3% 113 109 114 1.8 0.7
20 Luis Marte Tigers 17 0 26.0 20.0% 9.1% 117 111 66 -0.1 0.5
21 David Purcey – – – 111 21 206.0 18.8% 12.8% 118 108 116 1.1 0.3
22 Bill Murphy – – – 18 0 17.2 10.1% 19.0% 140 125 89 -0.2 0.2
23 Robert Ray Blue Jays 7 4 28.0 13.5% 9.2% 117 118 94 0.1 0.2
24 Willie Eyre – – – 111 2 163.2 11.9% 9.0% 115 108 109 0.2 0.2
25 Humberto Sanchez Yankees 2 0 2.0 12.5% 25.0% 134 119 104 0.0 0.0
26 Donnie Veal – – – 100 0 64.2 23.8% 16.0% 111 103 118 0.3 -0.1
27 Shane Lindsay White Sox 4 0 6.0 17.7% 14.7% 128 135 283 0.0 -0.2
28 Jared Wells – – – 8 0 8.1 11.4% 15.9% 147 183 210 -0.2 -0.3
29 Jack Egbert – – – 3 0 3.1 0.0% 10.0% 150 195 468 -0.1 -0.3
30 Joe Martinez – – – 21 6 55.2 12.0% 7.9% 111 109 144 0.2 -0.7
31 Virgil Vasquez – – – 19 10 61.1 12.5% 8.0% 121 140 154 -0.4 -0.7
32 Scott Mathieson Phillies 15 8 44.0 15.7% 9.7% 116 123 148 0.0 -0.9
33 Bryan Augenstein – – – 12 2 22.2 10.7% 8.0% 126 126 199 -0.1 -0.9
34 Clint Nageotte Mariners 16 5 41.2 12.3% 14.2% 120 129 176 -0.1 -1.0
35 Hayden Penn – – – 33 15 82.1 12.4% 13.4% 131 153 218 -0.9 -3.5

And here are the 22 members of the low-strikeout group to have recorded at least one major-league appearance:

# Name Team G GS IP K% BB% xFIP- FIP- ERA- WAR RA9-WAR
1 Mike Minor Braves 111 110 652.2 20.7% 6.9% 102 103 108 6.9 6.2
2 Jared Hughes Pirates 170 0 183.0 15.5% 8.0% 102 109 80 -0.6 1.4
3 Mitchell Boggs – – – 241 15 316.2 16.7% 10.3% 107 108 105 0.4 1.0
4 Anthony Swarzak Twins 181 32 439.2 14.2% 6.7% 111 103 110 2.1 1.0
5 David Pauley – – – 91 20 209.2 13.2% 7.4% 107 114 114 0.2 0.9
6 Brooks Brown Rockies 28 0 26.0 20.2% 4.8% 87 86 65 0.2 0.4
7 Stuart Pomeranz Orioles 3 0 6.0 11.5% 3.9% 92 113 72 0.0 0.1
8 Steve Garrison Yankees 1 0 0.2 0.0% 0.0% 121 73 0 0.0 0.0
9 Randor Bierd Orioles 29 0 36.2 14.0% 10.7% 121 105 110 0.1 0.0
10 Sean West Marlins 22 22 112.2 15.2% 9.3% 114 107 119 1.0 0.0
11 Jeff Marquez – – – 4 0 5.0 8.7% 0.0% 98 113 126 0.0 0.0
12 John Koronka – – – 31 30 158.1 10.7% 9.3% 122 118 135 1.0 0.0
13 Evan MacLane Cardinals 2 0 1.0 0.0% 25.0% 182 488 230 -0.2 -0.1
14 Chris Smith – – – 50 0 67.2 17.8% 9.3% 116 144 121 -0.8 -0.2
15 Jordan Tata Tigers 11 3 28.2 10.9% 11.6% 130 109 152 0.1 -0.3
16 Mitch Talbot – – – 43 41 232.2 12.3% 10.3% 120 124 132 0.5 -0.5
17 Brian Burres – – – 106 56 358.1 13.6% 9.7% 120 117 132 1.8 -0.5
18 Kevin Mulvey – – – 10 4 27.1 14.5% 10.7% 118 157 180 -0.3 -0.5
19 Lucas Harrell – – – 88 62 401.2 14.9% 11.1% 112 114 122 2.0 -0.6
20 Mike Parisi Cardinals 12 2 23.0 10.7% 12.4% 134 121 197 -0.1 -0.8
21 Chris Lambert – – – 14 3 33.0 15.9% 8.5% 116 138 165 -0.2 -0.9
22 Fernando Rodriguez – – – 126 0 132.1 24.2% 11.7% 110 110 119 0.0 -1.0

Five observations from the data:

• Among the high-strikeout group, 35 of 42 pitchers (83%) have recorded at least one major-league appearance. Among the low-strikeout group, only 22 of 43 pitchers (51%).

• Among the high-strikeout group, 7 of 42 pitchers (17%) have both (a) recorded the majority of their major-league appearances in a starting capacity and also (b) produced a strikeout rate above 20% (i.e. roughly the league-average rate). Only 1 of 43 pitchers (2%) from the low-strikeout group (Atlanta’s Mike Minor) has done the same.

• Among the high-strikeout group, 6 of 42 pitchers (14%) have recorded a 10 RA9-WAR or better. Zero pitchers among the low-strikeout group have reached the 10-win threshold. (Mike Minor’s 6.2 mark is the best such figure. No other low-strikeout pitcher has recorded more than two wins by this measure.)

• Pitchers from the high-strikeout group have compiled a collective 167.3 RA9-WAR, or 4.0 wins per pitcher. The low-strikeout group has produced just a 5.6 RA9-WAR collectively, or 0.1 wins per pitcher.

• Of more trivial interest, one finds right-hander Tommy Hanson produced the best strikeout rate among the relevant sample, recording a 48% strikeout rate (15.4 K/9) over 28.2 innings in 2008 — the best such mark by a considerable margin. Here are the top-10 AFL seasons by strikeout rate from 2005 to -09 among pitchers who faced at least 70 batters and registered at least half their appearances in a starting capacity:

# Name Year TBF K%
1 Tommy Hanson 2008 102 47.9%
2 Jered Weaver 2005 105 33.3%
3 Phil Hughes 2008 124 30.6%
4 Bill Murphy 2005 119 30.4%
5 Glen Perkins 2005 130 30.0%
6 Scott Mathieson 2005 120 29.9%
7 Stephen Strasburg 2009 77 29.8%
8 David Purcey 2007 87 28.7%
9 Brian Matusz 2008 109 28.4%
10 Luis Marte 2008 78 28.4%

And here, for some reason, are the 10 worst such seasons by that same criteria — a collection of players who’ve had less (if any) success at the major-league level:

# Name Year TBF K%
1 Stuart Pomeranz 2006 88 3.4%
2 John Koronka 2006 73 5.5%
3 Corwin Malone 2006 106 6.6%
4 Ryne Lawson 2008 76 7.9%
5 Jon Asahina 2005 122 8.2%
6 Josh Shortslef 2006 75 9.3%
7 Kevin Mulvey 2006 70 9.9%
8 Mark Roberts 2005 119 10.1%
9 Matt Peterson 2005 109 10.1%
10 James Simmons 2009 107 10.3%

*****

What have we found here? Well, what we’ve definitely found is that, among AFL pitchers from 2005 to -09 who both (a) faced 70 or more batters and also (b) made at least half their appearances as a starter — among that population, the pitchers who recorded a strikeout rate among the league’s top third have achieved greater future success, both graduating at a higher rate to the majors (about 80% vs. 50%) and producing more wins at the major-league level (about 30 times more wins). What we’re incapable of saying for sure is how predictive this data is — or, phrased differently, how it applies precisely to the pitchers currently participating in the Arizona Fall League. What it probably means, though, is that Baltimore’s Zach Davies, Miami’s Anthony DeSclafani, and Pittsburgh’s Joely Rodriguez (who are the candidates most likely to meet the criteria outlined above and finish in the top third of this year’s AFL by strikeout rate) are more likely to become successful major leaguers than Boston’s Keith Couch, Atlanta’s Aaron Northcraft, or Washington’s Felipe Rivero (who are most likely to finish in the bottom third, at this point).





Carson Cistulli has published a book of aphorisms called Spirited Ejaculations of a New Enthusiast.

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Pirates Hurdles
Guest
Pirates Hurdles

Isn’t this just restating what we already know; pitchers who strike out a lot of minor leaguers (particularly in the high minors) are better prospects than those who do not?

Pirates Hurdles
Guest
Pirates Hurdles

PS – Joely having a high K rate this Fall is almost shocking considering his complete inability to do so in his minor league career, then you realize it is 13 innings.