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All-time K/BB ratio

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.

This entry was posted on Tuesday, June 22nd, 2010 at 5:49 am and is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

11 Responses to “All-time K/BB ratio”

  1. Wade Robbins Says:

    Your points are all correct in explaining this phenomena. I would like to add one more that I think is a common attitude. Pitchers today pitch away from contact. Very few pitch with the purpose being a weakly hit ball. Many pitchers in the past would pitch with the objective being an off-balance swing and a weak hit. Examples of this were Mark Fidyrch, Oral Hershiser, and Greg Maddux. (Also, Mike Cuellar and, even, David Wells) This is just an observation which can only be backed up by your graph.

  2. The dip in K rate was 1988, not 1987. 1988-92 was a period of low offense era so it seems strange it was a period of lower strikeouts.

    I've read about the post-WWII walk boom before, but I've never heard about the large drop in K-rates in the late 1910s. I wonder what caused that.

  3. "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."

    If the offense is receding, wouldn't be expect the strikeout rate to increase?

  4. DavidRF, thanks that makes a lot more sense actually. I have adjusted the text above.

    Ellis, strikeouts tend to be correlated with offense. In other words, when offense goes down, it's not usually because strikeouts have gone up. It's usually the opposite--when offense is up, players are more free-swinging, which leads to both more runs and also more strikeouts.

  5. Bryan Mueller Says:

    Is there a significant difference between strikeout rates for pitchers in the National League compared to that of the American League since the DH? Over the course of the season, pitchers do get a good number of at-bats so I was wondering if that would show up on a graph comparing pitchers from both leagues.

  6. Bryan, yes there is a difference. I will post it in graph form later today or tomorrow.

  7. Could pitch selection influence/explicate these numbers? I am but an amateur historian of the game, but didn't there used to be a kind of historic bias against the curve ball? And I believe Nolan Ryan remarks on how the game changed in the 1960's, with pitchers throwing far more breaking pitches and far fewer fastballs. Or is this just legend?

  8. Andy - I think there's a simple reason why 3000K is still very hard to achieve despite higher strikeout rates: people throw fewer innings. It's hard to get to 4000 IP (200 over 20 years) on 30-33 starts per year, especially if a pitcher is only expected to get through six innings.

    Also, these are harder innings in general. When anyone 1-9 can tag your pitches, there are no opportunities to coast through weak hitters and simply let them bounce it to the waiting infield. That's probably why people don't pitch to contact anymore... it's a shortcut to a conga line around the bases.

  9. One other thought on the reason for increased strikeouts: The expanded role of relief pitching. Most pitchers before 1950 or so tried to go 9 innings every time. My understanding is that relief pitchers were only used when absolutely. Today when a pitcher can throw at top speeds with his best stuff for 7 innings, and then 2 relievers throwing with their best stuff for one inning each, there is a higher likelihood of more strikeouts. I believe the specialization of pitchers could be a determining factor in the increase of strikeouts.

  10. I have to agree with Dan, there are tons of relievers (i.e. Lidge, Rivera) who have shockingly high K/9 ratios because they pitch so few innings

  11. I'm surprised that nobody has brought up what I think is the number one reason for increased strikeouts in modern times - the fact that there is far less of a stigma attached to batters striking out today than there used to be. Teams are starting to just accept that when you have a guy like Mark Reynolds, Adam Dunn, Ryan Howard, etc., he's going to strike out 200 or more times a year, and there's nothing really wrong with that, because the thought is that making these guys change their approach at the plate to strike out less isn't worth the potential side effect of decreased offensive production. More and more people are promoting the idea that in the grand scheme of things, a strikeout is just another out, no worse than any other out.

    In the past, the thinking was very different. Batters made more of a conscious effort to not strike out. It was an embarrassment to get struck out, and a matter of pride to at least put the ball in play. Guys would choke up on the bat, cut down on their swings, etc. You don't really see anybody doing that today, outside of the occasional throwback hitter like Juan Pierre, Jason Kendall, etc. The thinking has drastically changed, and unless that thinking changes back again for some reason, I don't see strikeouts going back down significantly anytime soon.