The first National League game ever played was in 1876. With constantly changing rules, the run scoring environment of this era fluctuates wildly compared to the following eras.
For example, an umpire crew was not formally required until 1879. In 1880, only 8 balls were in an at-bat were necessary for a walk. Four years later, in 1884, only 6 balls; It was not until 1889 that 4 balls became the standard.
Select Walks to see walks per game increase fairly steadily through this time.
Additionally, the distance of the mound to home plate was increased from 50 ft to 60 ft and 6 inches in 1893, significantly changing the difficulty of hitting.
Select Strikeouts per game or Homeruns per game to see these increase through the pre-1900's era.
In the Dead Ball Era we see overall scoring decrease from the Pre-1900's era when we look at Runs Per Game.
Homeruns initially decreased in the transition to the Dead Ball Era. The name 'Dead Ball Era' explains these depressions in run scoring and homeruns, as the quality and material of the baseball had a lot to do with the amount of runs scored at this time.
Until 1911, the baseball had a soft rubber core, compared to the more kinetic cork-cored model that replaced it. Games would also be played with the same ball until it was unusable. Nowadays the one game will use upwards of 50 brand new balls.
According to "The Strikeout Ascendant", the foul strike rule, adopted in 1901 and 1903 for the National and American Leagues respectively, was a huge contributor to the run suppression of the Dead Ball Era. The Foul Strike Rule is what made foul balls actually count as strikes, making hitting significantly more difficult.
Another important consideration regarding the difficulty of hitting is that pitches involving foreign substances eg. the spitball were legal. Unsurprisingly Strikeouts per game increases from the Pre-1900's Era until an unexplained late dip before the Live Ball Era.
The Live Ball Era began with any doctoring of the ball, eg. spitballs, being outlawed and with the replacement of dirty or scuffed balls during the game. The later change was enacted largely in reaction to Ray Chapman's death, who was hit in the head with a scuffed baseball that got away from the pitcher. The ball also became arguably harder and more kinetic when new yarn began to be used in its manufacturing.
Select Strikeouts to see a decline in the strikeout rate from the Deadball Era into the Live Ball Era, thanks to balls having more predictable movement due to these changes.
We also see a clear increase in Runs Per Game from the Dead Ball Era, with teams sometimes scoring over 5 runs a game after scoring fewer than three over the course of certain years previous. Additonally, an enormous jump in Homeruns occured between the Dead Ball era into the Live Ball Era. The average homerun rate more than doubled from 1918 to 1922.
Also within the Live Ball Era was an isolated impact on the game due to many good players fighting in WWII. Runs and Homeruns sharply declined from 1940 to 1943 as a result.
On April 15th, 1947, Jackie Robinson broke Major League Baseball's Color Barrier. Robinson debuted with the National League's Brooklyn Dodgers and won Rookie of the Year. Only months later, Larry Doby became the first black player to play in the American League with the Cleveland Indians. These two pioneers, among others, sparked baseball's integration era.
The integration era was a time of fundamental change in baseball. If we look at Homeruns, we can see that homerun production exploded. Hitters started hitting with significantly more power, as the average homerun rate climbed to .84% in 1950, shattering the previous high from 1940 at .64%. The average homerun rate climbed even higher to .95% by the end of the Integration Era in 1961.
At the same time, we see Strikeouts climbed at a similar pace.
It's clear that hitters' approaches were changing; They became less contact/slap oriented and more geared towards swinging for the fences. The approach was high risk/high reward, reflected in these increases in homeruns and strikeouts.
The Expansion Era begins in the 60's, characterized by an increasing number of teams. At this time, the American League added two new teams: the Los Angeles Angels and the Washington Senators. The new Senators team replaced a former Washington Senators team that moved to Minnesota to become the Minnesota Twins. The National League also added teams now known as the Houston Astros and the New York Mets.
We see that Strikeouts increased initially in the Expansion Era, before regressing closer to the levels at the end of the Integration Era. We also see Runs Per Game, Homeruns, and Walks decrease noisily from Integration Era levels in the Expansion Era.
These trends can be explained by an increase in the size of the strike zone in 1963. The strike zone was not returned to its previous size until 1969. The height of the pitcher's mound was also lowered by 5 inches in 1969.
Each of these rule changes significantly decreased pitchers' advantages over hitters. This is reflected in average strikeouts per game fairly steadily decreasing through the rest of the Expansion Era. We also see a sharp increase in homeruns from 1969 to 1970. Walks increased in 1969, likely due in large part to the tighter strikezone.
The Free Agent Era is unsurprisingly named so because in 1976, MLB owners agreed to let players become free agents on the conditions that they had played out their contracts and had at least 6 years of service time. This was a fundamental change in the ways rosters were constructed and teams built. Yet regardless of the introduction of Free Agency, the changes on the graph are likely driven mostly by other factors. According to Steve Treder's article, many new stadiums built around the time of the Free Agent Era were built with astroturf, rather than real grass, in the outfield. Additionally, outfields were being built with increased dimensions.
With bigger outfields and faster (fake) grass, teams tended to play smaller, quicker players rather than their larger power hitters. This explains an initial dip in Homeruns as well as Strikeouts, given these smaller players were less likely to sell out for the long ball and strike out a lot.
Yet by the 1980's, teams had almost universally ditched astroturf and returned to natural grass. This change lead to the return of power hitters. The results, as we can see, were jumps in homeruns and strikeouts as the 1970's turned into the 1980's.
The Steriod Era speaks for itself. Homeruns skyrocketed to all time highs as hitters became more power/strength oriented than ever, sometimes supplementing their training with performance enhancing drugs. Along with homeruns, Strikeouts also reached all time highs as hitters focused on homeruns. Runs Per Game was also at its highest rate since the height of the Live Ball Era.
The Steriod Era will always be considered an era of shame for the game of baseball, yet also an era of incredible excitement. In 1998, Mark McGwire shattered Roger Maris' single season homerun record of 61, hitting 70 for the St. Louis Cardinals. Only three years later, Barry Bonds infamously broke McGwire's record, hitting 73 long balls in 2001 for the San Francisco Giants. Both McGwire and Bonds were later found out to be users of performance enhancing drugs. As of this page's development, neither have been elected to the Baseball Hall of Fame.
In 2007, a former senator and diplomat, George Mitchell, released an MLB-commissioned report detailing MLB's ties to performance enhancing drugs. The report linked 89 names to performance enhancing drugs and the fallout included a large number of suspensions and a crackdown on the use of performance-enhancing drugs.
Homeruns per game had already begun to decline before the release of the Mitchell Report, but began declining more dramatically after its release. Runs Per Game began to decline significantly as well.
One should notice that something significant happened in 2015. Homerun numbers surged, out of nowhere, to rates not seen since the Steriod Era. In 2016, homerun rates increased even more to the highest level in the history of baseball. What changed? Pitchers theorized that the MLB started "juicing" the baseball midway through 2015 in order to increase homeruns and excitement. Many pitchers also claimed to be able to detect a difference in the feel of the ball. The MLB fervently denied this until 2018, when MLB Commissioner Rob Manfred acknowledged that something had changed in the composition of the balls, although not under the intention of the MLB. Nonetheless, the baseballs became more aerodynamic and homerun production soared.
A related factor in increasing homeruns is a phenomenon called The Launch Angle Revolution. This involves hitters intentionally trying to hit the ball in the air, rather than on the ground, in order to hit more doubles and homeruns.
We also see Strikeouts per game increase sharply and steadily in the contemporary era, due in part to the previously mentioned emphasis placed on hitting homeruns by more and more hitters. This increase is also partially explained by better pitchers throwing harder than they ever have in the past. The average fastball velocity was 93.1 MPH in 2017, compared to about 89 MPH in 2002. Players in general are better trained and more athletic than they have every been; It is an exciting time for baseball.
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