The year baseball changed

Here’s a graph of baseball data. There are three sets of data: the red circles occurred in the years 1902-1919; the black diamonds occurred in the years 1920-1946; and the yellow squares occurred in the years 1947-2012. All years are separated into the two leagues, so there are twice as many symbols as years. As you can see, the data sets are almost completely separate—there are no black diamonds hiding behind the yellow squares and only one black diamond behind the red circles:


What you see here are three changes in the fundamental relationship between slugging percentage (the bottom, horizontal, “x” axis) and the extent to which home runs drive slugging percentage (technically, home run bases as a percent of total bases, on the side, vertical, “y” axis). Before 1920, slugging percentages and home run rates were low, though there was a fairly strong relationship between the two. When slugging percentage went up, so did the totals bases contributed by home runs. (I’m trying to avoid cause-and-effect language here, but obviously home runs cause an increase in slugging—not vice-versa).

Between 1920 and 1946, slugging percentage and home run rates were much higher than in the previous era (all the data points are up and to the right), but the relationship between the two was weaker. Take a close look: the points are more spread out and the slope is flatter. During this period, batters increased their slugging percentage in somewhat less homer-centric ways. They hit more singles, doubles and triples. They were more versatile sluggers.

From 1947 on, however, increases in slugging percentages were closely associated with increases in home runs. Look again: the yellow squares are much closer together than in the second era, and the slope is steepest of all. And this is key, too: the overall range of slugging percentage was roughly the same in the second and third eras; it was the role of the home run that changed.

By the way, I just have to point out that slugging percentage isn’t a percentage at all. It’s total bases divided by at-bats. It’s a ratio. But good luck getting anyone to change what they call it.

We all know that home runs have become more important over the years of our game, but many of us (me included) have tended to point to 1920 as the key year of impact; the year that Babe Ruth made home runs the weapon of choice and changed baseball forever. Or we’ve referred to the late 1990s as the time in which home runs became so pronounced that they became caricatures, events almost without meaning because they occurred so often (and, it turns out, under shady circumstances).

Well, we were certainly right about 1920 and Babe Ruth (the one black diamond behind the red dots, by the way, is the 1920 National League, which took a year to catch up to the home run trend started in the junior circuit). But I, at least, had completely missed the impact of 1947. In a way, the home run deluge of the 1990s and early 2000s was just a continuing trend of something that started the same year that Jackie Robinson made his major league debut. The yellow squares move up and to the right as the years progress, but the basic relationship between home runs and slugging—the manner in which the two grow and shrink together—hasn’t deviated from how it worked in 1947.

So we have two turning points in the nature of baseball slugging: 1920 and 1947. Let’s compare the two.

In the decade before 1920, singles accounted for 59 percent of all total bases. Doubles accounted for 22 percent, triples for 13 percent and home runs for 6 percent of all total bases. Then along came Ruth. In 1920, home runs accounted for a stunning 56 percent of his total bases, lapping the field. Tillie Walker was second at 28 percent.

Tillie Walker, by the way, is a great study in how hitting changed in the wake of Ruth. When he was an outfielder with the A’s in 1918, Walker tied for the league lead (with Ruth) with 11 home runs. Four years later, at the age of 34, he hit 37 home runs, just second in the league. The story is that Connie Mack didn’t like all the home runs in the game and so moved the fences back at Shibe Park the next year. Walker lost his edge, played in only 52 games, was cut from the team, played six more years in the minors, but never saw major league action again.

Overall, the percent of total bases contributed by home runs in the 1920s doubled to 12 percent. On the other hand, batters like Ruth and Lou Gehrig put up tremendous batting averages, too. For instance, Ruth hit .393 in 1923 and didn’t even lead the league in batting. His career batting average was .342. He was a combination of Tony Gwynn and Mark McGwire. Overall, batting average in the 1920s was .285. .285. Average.

In the 1930s, the home run percentage rose to a bit more to 16 percent (by the way, doubles maintained their share of total bases during this time. Singles and triples decreased about the same number of points to offset the increased proportion of home runs). Batting average declined a bit to .279 and slugging percentage basically stayed even at .399. Jimmie Foxx, Ott and Hank Greenberg were archetypal sluggers of the age; Foxx was similar to Ruth in combining slugging and batting while Greenberg emphasized power a bit more, but their profiles were roughly similar.

Then came war in the 1940s, when the best players played in military bases instead of major league parks. The overall quality of baseball declined during that time, of course. Batting average dropped 20 points and slugging dropped 30 points from the previous five-year period. Home runs as a percent of total bases declined a bit to 15 percent.

And then came 1947. Players had returned from the war and the overall quality of play resumed. Batting average rebounded a bit, albeit not to pre-war levels. Slugging percentage, on the other hand, made a big jump, powered by the home run.

In the National League in 1946, slugging had been .355 and home run bases as a percent of total bases rose had been 15 percent. In the 1947 NL, they were .390 and 21.4 percent (a six-point jump!). Slugging returned to near-pre-war levels, but now powered by the home run instead of batting average, which remained relatively low at .265.

In fact, the New York Giants of 1947 set a major league record for most home runs by a team (221, now the 48th highest team total ever). They obliterated the previous team total of 182 home runs, set by the 1936 Yankees.

Slugging and home runs never looked back. In 1948 home runs as a percent of total bases fell back a bit to 20.9 percent, but then it increased to 22.5 percent and 25.9 percent in the following years. In four years, the home run rate rose a whopping ten points! For perspective, that rate has been roughly 25 percent for the past decade.

The American League was a little slower to catch on and its jump wasn’t as stark. The AL went from 17.0 percent in 1946 to 20.8 percent in 1950, and didn’t lead the NL in this regard until Maris and Mantle chased Ruth’s record in 1961 (the league rate was 20.6 percent that year; Maris’ was 66.7 percent). The American League is the reason you see some of those yellow squares linger with the black diamonds. If I were to graph only the National League, the difference would be more stark.

So I wondered…if 1947 is roughly the equivalent of 1920, is there a rough equivalent of Babe Ruth? Can we point to a singular person and performance that introduced the Three True Outcome era?

The answer is no, there was no singular character or hero pointing to a new way. Instead, allow me to introduce the following cast of characters—a troupe of batters responsible for this new way of hitting. The time is 1947, the stage is the National League, the scene of the first act is the Polo Grounds.

Revitalized old man: Johnny Mize was a great slugger in the ’30s. In 1939, he led the National League in batting (.349) and home runs (28). He hit 43 home runs the next year and still batted .316. In 1947, at the age of 34 and playing with the Giants, Mize reached career highs with 51 home runs and 138 runs batted in, leading the league in both categories, but his batting average dropped to .302 and would never be above .300 again. Perhaps the impact of aging, or a harbinger of what was to come?

One-shot star: Willard Marshall was a 26-year-old right fielder on the 1947 Giants team. He had reached the majors at the age of 21, showing a rifle arm and impressing manager Mel Ott, but then served three years in the Marines. He returned to the majors in 1946 and had a career year in 1947: 36 home runs (third in the league) with 107 RBIs and a .291 batting average. He played for eight more years, but never matched those numbers again.

Sturdy player has his moment: Walker Cooper was the catcher on that Giants team, and he set his own career mark with 35 home runs. During his time, Cooper was known as the best catcher in baseball, particularly with the Cardinals in the early 1940s. He had a fine 18-year career with a .285 batting average, but never had another home run year close to 1947.

Waiting for his destiny: Bobby Thomson was the Giants’ center fielder in 1947, his first full year in the majors. He hit .283 with 29 home runs but, unlike his slugging Giants teammates, Thomson also struck out a lot: 78 times in ’47 (Mize, Marshall and Cooper struck out 115 times among them.) Thomson had a fine career, including a moment of destiny against Ralph Branca.

The one who came before: Our two leading characters didn’t play in New York. Cubs outfielder Bill Nicholson led the league in strikeouts in 1947 (with a whopping 83 Ks) while batting .244 with 28 homers (hence his nickname, Swish). Nicholson was only the second player in baseball history to hit more than 25 home runs, bat less than .250 and strike out more than 80 times. (The first was Pat Seerey in 1946. Seerey deserves a bit part in our play.)

Nicholson had led the league in home runs and RBIs in 1943 and 1944 and played on the Cubs’ last World Series team. In 1950, after he was traded to the Phillies, it was disclosed that Nicholson suffered from diabetes.

Leading man: In 1947, Ralph Kiner was a 24-year-old Pirates outfielder in his second year in the majors. He had quite a year, batting .313 with 51 home runs (tying Mize for the league lead) and a .639 slugging percentage. He had led the league in strikeouts the previous year with 109, but managed to reduce the number to 81 in 1947.

By today’s standards, Kiner’s numbers look pretty well-rounded. He was no Dave Kingman (of whom Kiner once said “He can hit them out of any park—including Yellowstone”) or Adam Dunn. Not even a Harmon Killebrew. But he, and his cast of characters, set something in motion.

Consider the batting averages of the previous batters to hit 50 or more home runs before Kiner: Ruth did it four times and his batting averages were .376, .378, .356 and .323. Hack Wilson did it with a batting average of .356. Jimmie Foxx: .364 and .359. Only Greenberg, at .315 with his 58 home runs in 1938, had a batting average as low as Kiner and Mize did in 1947. Never again; only Mantle (in 1956, when he hit .353 with 52 home runs) would reach those heights again. Slugging had changed and would not go back. Ralph Kiner was the new prototype.

In some ways, baseball has never been better than it is today. The athletes are in terrific shape. The game is executed at a top level. Media coverage is spectacular and division races are terrific. Still, I wish I could have watched baseball in the ’20s and ’30s.

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  1. Marc Schneider said...

    But there is obviously a reason why batting averages declined.  Pitching improved. Home runs went up, at least in part, due to livelier balls and hitters swinging harder. Especially after World War II, you saw the introduction of new pitches-sliders apparently became more common-and, albeit more slowly, the increasing use of relief pitchers.  I doubt that even Babe Ruth today could hit .393 with 50+ home runs.  Moreover, this is a lesser differential in quality between teams, especially because of the color barrier. There were lots of really bad teams in the 20s and 30s; guys like Babe Ruth I’m sure feasted off pitchers that probably would not be in the majors today.

  2. Frank Jackson said...

    I’ve always been of a mind that there should be more singles than doubles, more doubles than triples, and more triples than home runs.  Somehow, with livelier baseballs and changes in ballpark architecture, we ended up with more home runs than triples.  Triples, in the days when they were more plentiful, were not a bad way to enhance one’s slugging percentage. 

    Henry Aaron once said that triples were more exciting than home runs.  I think he’s right.  You don’t see many stand-up triples.  There’s usually an element of suspense as to whether the guy’s going to make it or not.

    If ballparks were designed for more triples, that would also increase the possibility of inside-the-park home runs for speedier players.  That, of course, is the ultimate in excitement.  Unfortunately, that sub-species of four-bagger is all but extinct.

  3. Dave Cornutt said...

    So the $64K question is: What about the game changed in 1947?  We have a good idea of what happened in 1920; the ball changed.  But what about 1947?  Was it because a lot of the players served during WWII and learned a lot about physical fitness?  Was nutrition getting better?  Did the equipment change somehow?  Or was it just a matter of hitters figuring out a more effective mode of hitting?  I see the data.  Now I’m really curious about what’s behind it.

  4. Steve Treder said...

    I’ve long suspected that one of the reasons 1947 stands out is that they continued to use the Balata ball for part of the 1946 season, exhausting the inventory before introducing the pre-war spec baseball, and therefore the ‘46 stats are power-suppressed.

    But, as has been pointed out, a lot of factors were having impact simultaneously.  Hitters and pitchers were bigger and stronger.  Night baseball and the increasingly sophisticated use of relief pitchers drove down batting averages, but not so much home runs, and most everyone adapted to the new conditions to pursue their self-interest.  Thus a dynamic developed that rewarded the capacity to produce ever-more home runs (certainly including the fact that fans love them), and that engine operated in high gear until the mid-1960s.

  5. Professor Longnose said...

    Regarding ratios, what bugs me is the current habit of saying a pitcher has, eg, a 47K/13BB ratio. It’s just totals masquerading as a ratio. That’s not a ratio worth anything, because it isn’t standardized. Divide it through and give us a usable ratio, or just announce the totals!

    Or else! <shakes fist>

  6. Dennis Bedard said...

    There has to be an evolutionary/biological reason for this.  Human physical acheivement and body size increase over time.  Nutritional and medical advances allow people to live longer and healtheir lives.  The infant mortality rate has declined dramatically as the life expectancy rate has increased.  Look at basketball.  Gone is the two hand set shot.  The acrobatic dunk has replaced the humble layup.  Ditto football.  The size, speed, and strength of the players makes comparisons almost comical.  I think normal evolutionary human advances in strength and quickness favor a hitter over a pitcher.  I have no scientific evidence to back this up.  It is all third rate supposition but it seems as logical an explanation as any other.

  7. Steve Treder said...

    Evolution of the genetic code of a species takes place over hundreds if not thousands of generations.  What we’ve seen in the increased size and strength of athletes in sports isn’t evolution per se, but rather big changes in the nutritional/conditioning/medical environment, as well as greater selection capability (that is, bigger candidate pools) for the teams.

  8. Northern Rebel said...

    Sometimes I long for the strategy of the dead ball era. I would love to be transported back to a game and see Honus Wagner’s, or Ty Cobb’s magic with the bat, and on the basepaths.
    However, would I miss seeing Big Papi hit one 450 feet?
    You betcha!  :o)

  9. gdc said...

    I would think that going back to the dead ball era you would see more infield hits (balls knocked down and runner beats out throw, batter knocking two-hopper through gap like a tennis player whether a hit-and-run is on or not) and thinking that dropping in Omar Visquel or any of half a dozen current non-Gold-Glove shortstops onto your team would add four or five wins.  Unless the minor-league quality of groundskeeping caused them to also play in to avoid bad hops and lose a step.

  10. Marc Schneider said...

    It’s not evolution; it’s better nutrition and training, resulting, in part, from greater afflence in the society. Americans are bigger (maybe too big) because they have the money to eat more.  I don’t think there is any reason to think that human hand/eye coordination has changed. The change in baseball, to some extent, reflected changes in strategy-the home run seemed a more efficient way to play than playing for one run at a time.  And, not to get too speculative about this, with the US being a superpower after WWII, maybe the emphasis on power reflected how Americans saw themselves.

  11. Paul G. said...

    It is said that new, revolutionary ideas (or at least ones with merit) do not tend to catch on completely until the existing Old Guard, who have invested themselves in the old ideas and are less prone to change at this point, leave the scene (or die off, perhaps violently, as the case may be).  Baseball players can be as stubborn as anyone.  A baseball generation is roughly 20 years.  Player careers were typically not that long, but they become the next cohort of managers and coaches.  Take out the WWII interruption and 1947 is roughly 20 years from 1920.  It may just be the ultimate adoption of the home run philosophy was one of the factors here.

  12. Steve Treder said...

    Yes, the players entering the major leagues in the mid-to-late 1940s had been born in the 1920s.  They had no memory of the Dead Ball era, and had not grown up being coached in Dead Ball era techniques.  Swinging for the fences was the only way they’d ever played ball.

  13. Professor Longnose said...

    Perhaps the slider had something to do with it. To hit it, or not swing at it as it breaks away from the plate, means slowing down your swing and hitting fewer homers, But if you want to keep hitting homers, you’re going to have to swing early and accept a certain amount of swings and misses.

  14. Mac said...

    Fascinating discovery.

    Not sure this is telling the whole story though. I went through the data and made graphs of Hits, BB, 1B, 2B, 3B, and HR through time:

    Sorry about the graphs being out of order.

    HR rate has been rising mostly steadily. There was a dip during the war, but it looks pretty linear to me through to 1960, and then a dip for the extreme pitcher era. The continual HR lack in the 70’s/80’s is fascinating.

    As for HR as percent of slugging, in my album linked above I made the same graph, but for triples. The same pattern emerges. So are HR’s truly responsible for the increase, or is it more that triples dropped out of favor, thus increasing the relative proportion of everything else as a percent of total bases?

    I’m not actually totally sure about that last point, but there’s some correlation/causation concern here.

    All in all, fun to investigate.

  15. studes said...

    Thanks for the comments, everyone.  I agree that it’s fun to speculate about the reasons for this fundamental change, and I think folks have hit on the most likely culprits.  At least, I haven’t been able to think of others.

    For me, the fun part of the article was pinpointing a time in which this new type of hitting and pitching took root.  I mean, I was always aware of Kiner, Swish Nicholson and the change in baseball (Didn’t Bill James call the ‘50’s a time of crisis in baseball history, when the game became particularly boring?). But I hadn’t been quite fully aware of how the way we’re playing today is really just an extension of something that seemed to switch on over 60 years ago.

  16. Sabertooth said...

    Great write up! Here’s a question: after Mantle got to .350/50 in ‘56, who has gotten to either .350/40 or .340/50 since then?

  17. Roger said...

    Sabertooth, Bonds comes to mind…

    2002: .370 and 46 HRs
    2004: .362 and 45 HRs

    There may have been some others.

  18. Gyre said...

    Great read, and that certainly includes the comments.  I’d love to see a Dead Ball game or a dozen.

    I’d bet on a ball change and the huge increase potential players (WWII made travel easier, improved communication and education, and connected the West – plus Landis died).  Local newspaper has a Olde News column that runs thru the war, the amount of rationing is frightening, so I doubt better nutrition – that would have taken until the late 50s to kick in.

    As for triples, I certainly agree that they are more exciting due to the suspense.  Conservative play says that you can score from second, so stay there, thus less triples.

  19. Jim Clark said...

    baseball was just a few years away from a number of franchise moves after a half century of stability. Was this anticipated in the newspapers and magazines of 1947, or did it catch people by surprise?

  20. Steve Treder said...

    “Was this anticipated in the newspapers and magazines of 1947, or did it catch people by surprise?”

    There had been talk of franchise shifts before 1947.  Specifically the St. Louis Browns and the Philadelphia Phillies had been rumored to be looking at moving at a couple of points in the ‘40s.  But it had just been talk, never all that seriously developed.

    Still, the notion of big change was in the air in the immediate post-war years.  The Pacific Coast League was actively lobbying to be recognized as a third major league, largely because PCL owners feared that unless they did that, NL/AL teams would move in to their territory.  It was an era in the US of anticipation of major progress, powerful modernity, new big things.

  21. wsk said...

    i think that gyre has a very good point: in 1947-8, there were, effectively, two generations of good baseball players showing up.
    the ones who were good in 1941, and the ones who became good in the interim. better hitters.
    pitchers have never controlled homes runs; batters, balls & parks do.
    and going back to the rubber wound ball had an enormous effect.
    the senators didn’t hit an out of the park homer in 1945, i believe.
    very heavy ball.

  22. KJOK said...

    I think the 1920’s had a shift where it was OK to swing harder (until 2 strikes), but around 1947 the strategy was expanded upon, adding it was OK to PULL the ball.  Only 2 ballparks had been built since the deadlball era, and those old parks mostly had short distances down the lines but deep center field distances.  I don’t think it’s a coincidence that it was the NY Giants in the Polo Grounds that led the way in changing the mix of HRs to extra base hits.

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