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July 24, 2007

Prospectus Toolbox

Non-contact, Part One

by Derek Jacques

Statheads and strikeouts…it's an age-old romance. For pitchers, we'll tell you that strikeouts are the biggest predictor of a hurler's future success. When batters go down, though, while we acknowledge that the whiff is an out--a negative result--it's an out we put on a pedestal as one of the Three True Outcomes (along with the walk and the homer). A noble out, I guess.

Where does this love for the breezy out come from? Part of it is certainty. One big reason that dissecting baseball data is so rewarding is the peculiar one-on-one matchup between pitcher and batter, a rarity in team sports. The strikeout is the pitcher's ultimate victory in that confrontation, leaving the batter grumbling as he walks back to his dugout, rather than running the bases. It's conclusive. Even better, it's simple. Remember all that trouble we have measuring defense? It's largely academic when the only fielder involved has a catcher's mitt. The issue of whether or not a pitcher is able to control the destiny of balls in play is irrelevant if you keep the batter from making contact with the ball.

Now, glovework does still come into play on the strikeout, and it's possible for the batter to reach base even on a humiliating whiff. However, it's exceedingly rare--over the past 47-plus seasons, the batter reached base safely on 0.3 percent of all strikeouts. By way of comparison, this season a batter who hits a ball in play has a more than 30 percent chance of reaching base safely.

Strikeout rate is one of the performance metrics that shows the most consistency from one season to the next. Correlation studies, such as this one by James Click, show that once a pitcher shows a tendency to record strikeouts, they're likely to maintain that level--much more likely than they are to maintain their ERA or batting average on balls in play allowed. That's why power pitchers are very generally considered better bets to repeat their performance than pitchers who induce a lot of contact--their strikeouts can be considered a reliable source of high-percentage outs, which they're expected to carry over from year to year.

The stat that we most frequently look at when talking about pitcher strikeouts is strikeouts per nine innings (SO/9). This measure is a little quaint--we're pretty close to the point where complete games are so rare that the number of strikeouts a pitcher would record in nine innings is an abstract concept--but it's the standard. Let's take a quick look at the best seasons since 1959, by strikeout rate (min. 162 IP):


Year  Name             Age     IP     SO   SO/9  SO Rate
2001  Randy Johnson     37    249.2  372  13.41  .3743
1999  Pedro Martinez    27    213.1  313  13.20  .3749
1998  Kerry Wood        21    166.2  233  12.58  .3333
2000  Randy Johnson     36    248.2  347  12.56  .3467
1995  Randy Johnson     31    214.1  294  12.35  .3395
1997  Randy Johnson     33    213    291  12.30  .3424
1998  Randy Johnson     34    244.1  329  12.12  .3245
1999  Randy Johnson     35    271.2  364  12.06  .3374
2000  Pedro Martinez    28    217    284  11.78  .3476
2002  Randy Johnson     38    260    334  11.56  .3227
1987  Nolan Ryan        40    211.2  270  11.48  .3093
1984  Dwight Gooden     19    218    276  11.39  .3140
1997  Pedro Martinez    25    241.1  305  11.37  .3221
2003  Kerry Wood        26    211    266  11.35  .2999
1989  Nolan Ryan        42    239.1  301  11.32  .3047
1997  Curt Schilling    30    254.1  319  11.29  .3162
2001  Kerry Wood        24    174.1  217  11.20  .2932
1995  Hideo Nomo        26    191.1  236  11.10  .3026
2002  Curt Schilling    35    259.1  316  10.97  .3107
2004  Oliver Perez      22    196    239  10.97  .2969
1993  Randy Johnson     29    255.1  308  10.86  .2953

This list is sorted by SO/9, but I've also given you a superior stat, strikeout rate (SO Rate), which does more or less the same thing. SO Rate is strikeouts per batter faced, a measure that gives you a better idea of a pitcher's strikeout dominance than strikeouts per inning does.

To illustrate this point, we can look at two players on the top 20 above, Kerry Wood and Curt Schilling. By SO/9, Wood's 2003 was better than Schilling's 1997, and Wood's 2001 was better than Schilling's 2002. Schilling's SO Rate in each of those two seasons (.3162 and .3107) was better than Wood's in either of his (.2999 and .2932), because Schilling was facing far fewer batters per inning than Wood was.

The other thing you've likely noticed is that the SO/9 top 20 is dominated by pitching performances from the last 12 years. The highest-ranking pitcher season from the pitching-dominated sixties, Sudden Sam McDowell's 1965 (10.71 SO/9), comes in at number 22 in this ranking. Nolan Ryan's 1973 (10.57 SO/9) is the first representative from the '70s, at number 25. Some of that is a convergence of great strikeout pitchers--Randy Johnson, Pedro Martinez, Wood, Schilling--but another element is that the period since the 1994 strike has seen a historic increase in strikeout levels in the majors.


Years         MLB SO Rate
1960-1969       .1509
1970-1979       .1348
1980-1989       .1406
1990-1999       .1592
2000-2007       .1675

One way we can adjust for the change in strikeout rates across the eras is to normalize these values to a single standard. This is exactly what the Davenport translations do, presenting normalized strikeout rates (EqSO/9) on the DT Player cards. This way, we can look at the best strikeout seasons of all time, on an even playing field:


Name                Year  Team   EqIP  EqSO  EqERA  EqSO/9
Pedro Martinez      1999 BOS-A  259.2   382   2.15    13.2
Rube Waddell        1900 PIT-N  173.1   252   3.58    13.1
Rube Waddell        1902 PHI-A  220.2   316   2.49    12.9
Dazzy Vance         1926 BRO-N  168.1   237   3.90    12.7
Johnny Vander Meer  1941 CIN-N  225     310   3.36    12.4
Sandy Koufax        1960 LA-N   175     240   4.22    12.3
Rube Waddell        1903 PHI-A  270.1   370   3.43    12.3
Randy Johnson       1998 SEA-A  184.1   249   4.20    12.2
Randy Johnson       1992 SEA-A  224.2   302   4.17    12.1
Randy Johnson       1995 SEA-A  273.2   368   2.33    12.1
Randy Johnson       1997 SEA-A  235.2   316   2.29    12.1
Randy Johnson       2001 ARI-N  284.2   383   2.59    12.1
Dazzy Vance         1925 BRO-N  258     347   3.24    12.1
Pedro Martinez      2000 BOS-A  261     349   1.76    12.0
Rube Waddell        1904 PHI-A  264.2   351   2.92    11.9
Dwight Gooden       1984 NY-N   240.2   316   3.44    11.8
Sam Jones           1956 CHI-N  182     238   4.05    11.8
Sandy Koufax        1961 LA-N   270     350   3.63    11.7
Dazzy Vance         1924 BRO-N  299.2   391   2.58    11.7
Rube Waddell        1907 PHI-A  216.2   282   4.53    11.7
Lefty Grove         1926 PHI-A  255.2   329   2.99    11.6
Van Lingle Mungo    1936 BRO-N  289.2   374   3.42    11.6
Johnny Vander Meer  1942 CIN-N  242.2   312   3.26    11.6
Randy Johnson       1993 SEA-A  274.1   352   3.05    11.5
Cy Seymour          1898 NY-N   258.1   330   4.01    11.5
Dizzy Dean          1933 STL-N  274.1   347   3.74    11.4
Randy Johnson       2000 ARI-N  278     352   2.72    11.4
Nolan Ryan          1989 TEX-A  258.2   328   3.55    11.4
Kerry Wood          1998 CHI-N  184     234   3.33    11.4
Nolan Ryan          1978 CAL-A  223     279   4.16    11.3

Using the normalized figures, we see the addition of a number of seasons that were outside of the previous search, but we also see a good bit of movement within the previous list's time frame. Most notably, Sandy Koufax's 1960 season pole-vaults past Randy Johnson's cluster of dominance to fall into sixth place (based on raw stats, it was 45th); Koufax's 1961 and Nolan Ryan's 1978 both make it into the top 20.

Beyond enabling us to take a better look at individual pitchers' seasons across eras, EqSO/9 is also a fine tool for comparing team's strikeout rates over the years. We'll pick up there in part two of Toolbox's tribute to the strikeout.

This article would not have been possible without research contributed by William Burke and Clay Davenport.

Further Reading

Rany Jazayerli, "Doctoring the Numbers-Ballardesque Strikeout Ratios": A look at pitchers with extremely low strikeout rates.

Nate Silver, "Lies, Damned Lies-Strikeout Rate, Redefined": The debut of Nate Silver's signature stats column dealt with the difference between strikeouts per nine innings and strikeout rate.

James Click, "Baseball Prospectus Basics-Statistical Consistency": This study showed the level of year-to-year consistency of various statistical measures by measuring their correlation coefficients over the period from 1991 to 2003. Among pitching statistics, SO/9 and groundball/flyball ratio were the ones that showed significant year-to-year consistency.

Nate Silver, "Lies, Damn Lies-Secret Sauce": Explaining the relationship between a team's normalized strikeout rate (EqSO/9) and their postseason success. For more on this subject, you can also review Silver's chapter (with Dayn Perry) in Baseball Between the Numbers, entitled "Why Doesn't Billy Beane's [Expletive Deleted] Work in the Playoffs?"

Derek Jacques is an author of Baseball Prospectus. 
Click here to see Derek's other articles. You can contact Derek by clicking here

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