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).