Since 1890, these are the largest annual changes in strikeout percentage:

  • 1893, -38%
  • 1901, +32%
  • 1903, +21%
  • 1946, +20%
  • 1918, -17%

And these are the largest annual declines in strikeout percentage since 1890:

  • 1893, -38%
  • 1918, -17%
  • 1899, -10%
  • 1917, -9%

The three largest changes in SO% correspond with major rule changes. In 1893, the pitching distance was increased to 60′ 6″, and strikeouts plummeted. In 1901, the foul-strike rule was adopted by the National League, and the American League followed suit in 1903, with each move bringing a large rise in strikeouts.

The 1946 spike likely has much to do with the postwar return of the regular players — notably Bob Feller, whose 348 Ks in 1946 were one shy of the modern record and accounted for 22% of the raw SO increase over 1945 — and of regular ball-making materials. It still represents an 8% rise compared to 1940, which in turn was the highest rate since 1916. Hal Newhouser, perhaps the most notable holdover from wartime, averaged 5.4 SO/9 in 1944 and 6.1 in ’45, then surged to 8.5 SO/9 in 1946.

But what caused the large drop in SO% in 1917-18?

__________

By 1903 both leagues had adopted the foul-strike rule, and from then through 1916, the MLB strikeout percentage ranged from 9.5% to 10.8%, with no annual change greater than 7%. But in 1917 the rate dipped by 9% — the 4th-biggest drop in modern times — to reach its lowest mark since 1902. A further plunge of 17% in 1918 — the biggest drop outside of the sea change brought by the modern pitching distance — lowered the rate to 7.7%, the lowest since either league counted fouls as strikes. That was 25% below the 1916 rate, and 23% below the 1903-16 average.

Here’s a chart, for you visual types. I’m told that 1917 is purple and 1918 is red:

MLB SO Pct 1904-33

 

The effect was seen broadly:

  • The AL rate fell by 22% from 1916-18, the NL rate by 27%.
  • Out of 97 batters with 200+ PAs in both 1916 and 1918, 70% saw their SO rate fall at least 20% over the two years, while just 3% had a rise of 20% or more. A dip of at least 10% was 11 times as common as a similar increase (80% vs. 7%).
  • Out of 61 pitchers with 50+ IP in both 1916 and 1918, 72% saw their SO rate fall at least 20% over the two years, while just 5% had a rise of 20% or more. A dip of at least 10% was 10 times as common as a similar increase (84% vs. 8%).
  • In 1916, the top 10 marks in SO/9 ranged from 5.9 to 4.7; the 1918 range was 5.2 to 3.6. And note the progression of the 1916 SO/9 leaders; every one declined in 1917 and again in 1918:
Rk 1916 1917 1918
1 Larry Cheney 5.9 4.4 3.7
2 Walter Johnson 5.6 5.2 4.5
3 Allen Russell 5.5 4.7 3.4
4 Lefty Williams* 5.5 3.3 2.6
5 Harry Harper* 5.4 5.0 2.9
6 Tom Hughes 5.4 4.9 n/a
7 Elmer Myers 5.2 3.9 1.6
8 Bullet Joe Bush 4.9 4.7 4.1
9 Claude Hendrix 4.8 3.4 3.3
10 Fred Anderson 4.7 3.8 3.1
11 Dutch Leonard* 4.7 4.4 3.4
12 Al Mamaux 4.7 2.3 n/a
13 Rube Marquard* 4.7 4.5 3.4
14 Babe Ruth* 4.7 3.5 2.2
“n/a” = less than 70 IP
Table provided by Baseball-Reference.com.

But what was the cause? I’ve been searching all day, but I haven’t found it yet.

The size and breadth of the SO drop suggests some change in basic conditions. If the ban on doctored baseballs and the practice of keeping a fresher ball in play could be dated to 1917-18, that alone might explain the decline in strikeouts. But every source I can find dates those changes to the period of 1919-21, and especially to the death of Ray Chapman in August 1920.

The 1918 season was shortened by a month due to World War I, but I can’t see how the lack of September baseball by itself would affect strikeout rates. And while some players did lose time to WWI service or to defense-related jobs, the numbers were nothing like what was to come in the next war.

During 1917-18, there was no change in the official strike zone definition, nor any other significant rule changes to the game on the field.

I can’t rule out changes in visibility at existing stadiums, but no team changed parks from 1916 to ’18.

It’s interesting that the drop in strikeouts was not matched by a significant rise in batting average. The 1916 BA was .2476, rising to .2538 in 1918, a gain of just 2.5%. By comparison, the 1893 drop of 38% in SO% was accompanied by a 14% rise in BA, and the 1899 drop of 10% in SO% came with a 4% rise in BA. It’s also curious that home-run percentage fell by 25% from 1916 to 1918, but slugging average was virtually unchanged.

Whatever the causes, the 1918 strikeout rate became the “new normal.” The MLB SO% stayed between 6.9% and 8.2% from 1918 through 1933.

If you have any ideas on the cause of the 1917-18 drop in strikeouts, let us hear them!

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