Posted by Andy on June 22, 2010
Let's take a look at historical values for strikeouts and walks per 9 innings. I would imagine that some readers are very familiar with this data while it's new for others. I personally had never looked at the numbers in detail and was flabbergasted by the results.
Let's jump right in with the graph showing overall strikeouts per 9 innings pitched, walks per 9 innings pitched, and the ratio of strikeouts per walk. These numbers are across all of MLB for each season.
First some general comments on what we see above:
- For the period 1920-1950, strikeouts and walks closely correlated. As you can see, their ratio (SO/BB) was essentially exactly 1.0 for that entire period.
- In the 1950s and 1960s, strikeouts went consistently up while walks went consistently down. The ratio gradually climbed from 1.0 to 2.0, meaning double the number of strikeouts per walk.
- In the 1970s, strikeouts fell while walks remained pretty constant. The ratio fell to about 1.5.
- Since then, strikeouts have gone up almost every season while walks have remained pretty much unchanged. The ratio has gradually climbed back to 2.0.
- A few years stick out as interesting:
- 1969: The low offense in 1968 triggered the lowering of the pitching mound to 10 inches. Interesting to note that walk rate jumped dramatically between 1968 and 1969, suggesting perhaps that pitchers were having trouble with control using the new mound.
- 1988: This is one of the few seasons since 1981 when the strikeout rate dropped relative to the preceding season. As we know, offense (and HR in particular) were significantly up in 1987, and when offense dropped in 1988 so did the strikeouts.
- 1992/1993: As with many other indicators for the Steroids Era (which began in 1993), the strikeout rate went down in 1992, but then started its climb in 1993. Walk rate also started a (albeit less dramatic) climb in 1993.
- 2001-present: Many offense numbers from the last 20 seasons peaked in 2001, and indeed strikeout rate hit a peak in 2001. However after falling back a bit in the years after 2001, it has gone back on the climb in the last several years. It's also notable that the walk rate plunged in 2001, I suspect because batters were quite intent on putting the ball in play and hoping for a home run.
Reasons for the gradual climb in strikeouts are likely many, but three significant factors stick out in my mind:
- Better strength and mechanics for today's pitchers, yielding more guys who throw hard and are prone to strike out batters more often, plus a greater emphasis on this type of pitcher in scouting and development
- More emphasis on the home run and swinging for the fences--this goes hand in hand with discussions in other threads about the gradual disappearance of light-hitting, good-defense players in favor of guys who can hit for extra bases
- Less emphasis on "small ball", meaning sacrifice bunts and advancing of runners. These strategies put the ball in play (meaning no strikeout) and when they are not used as often, the door is opened for the batter to strike out instead.
Strikeout rates also came up as part of the Curt Schilling Hall of Fame discussion, with a few folks taking the position that Schilling's 3000 strikeouts were not as impressive as they used to be given the climb in strikeout rate. Let's just do some quick math. With a K rate around 7 per 9 innings, an average pitcher today would need to throw about 3,860 innings to reach 3,000 strikeouts. (That is a drastically oversimplified calculation, of course, since a guy who throws that many innings would likely be well above average for a good chunk of his career, plus below average for some of it.) Back when the K rate was closer to 5 per 9 innings, an average pitcher would need to throw 5,400 innings to reach 3,000 strikeouts. That is indeed a big difference, but either way you look at it such large inning and strikeout totals are such rare events that they deserve to each be looked at in their own context. Even with strikeouts so much more common these days, very few pitchers approach the 3,000 mark.
I wonder how much higher the strikeout rate can go. Keep in mind that people must have been wondering this in 1964 as well. At that time, the K rate had climbed consistently for 13 years from about 3.8 in 1951 to 5.9 in 1964 (an increase of 55%--that would be like today's rate of 7 climbing to nearly 11 strikeouts per 9 innings!) But sure enough, starting around 1965, the rate started dropped and gave up much of that increase over the two decades that followed.
We need to remember that example when thinking about the future. Much of the data for 2010 shows that offense is receding and I would not be terribly surprised to see the strikeout rate start to drop over the next several years.