MLB: What Exactly Happened To Offense In the 1990s
Expanding Horizons
Baseball has been adding teams since it began, so that’s nothing new, but since World War II, it has been notable that each expansion has done some drastic changing to the offense in that time period immediately following the expansion.
Statistically speaking, here’s what we are looking at 5 years and 10 years post-expansion. The number differentials are in relation to the year before expansion took place. For instance, the numbers you see cited for the 1993 expansions relate to what the numbers were in 1992 when reflecting on 1998 and 2003 following the expansion, not on the numbers in 1993.
Runs per Game
1961: +0.22, 1966: -0.32, 1971: -0.42
1969: +0.65, 1974: +0.7, 1979: +1.14
1977: +0.48, 1982: +0.31, 1987: +0.73
1993: +0.48, 1998: +0.67, 2003: +0.62
1998: +0.02, 2003: -0.04, 2008: -0.12
Home Runs per Game
1961: +0.09, 1966: -0.01, 1971: -0.22
1969: +0.19, 1974: +0.07, 1979: +0.11
1977: +0.29, 1982: +0.22, 1987: +0.48
1993: +0.17, 1998: +0.32, 2003: +0.35
1998: +0.02, 2003: +0.05, 2008: -0.02
Batting Average
1961: +.003, 1966: -.006, 1971: -.006
1969: +.011, 1974: +.020, 1979: +.028
1977: +.009, 1982: +.006, 1987: +.008
1993: +.009, 1998: +.010, 2003: +.008
1998: -.001, 2003: -.003, 2008: -.003
On Base Percentage
1961: +.004, 1966: -.014, 1971: -.007
1969: +.021, 1974: +.025, 1979: +.031
1977: +.009, 1982: +.004, 1987: +.011
1993: +.010, 1998: +.013, 2003: +.011
1998: -.002, 2003: -.004, 2008: -.004
Slugging Percentage
1961: +.011, 1966: -.012, 1971: -.023
1969: +.029, 1974: +.039, 1979: +.057
1977: +.040, 1982: +.028, 1987: +.054
1993: +.026, 1998: +.043, 2003: +.045
1998: +.001, 2003: +.003, 2008: -.003
It is notable that while run scoring has progressed over time in baseball, meaning the baseline for each of these expansions is different, the effect of the expansion on run scoring has been notable, and in the time period in question, baseball experienced two expansions, in 1993 and in 1998 with two teams added each time.
What is noted in multiple studies is that while expansion certainly adds players of lower quality to both the hitting and pitching pools, generally, the elite pitchers produce as they always did while elite hitters tend to beat up on the lesser pitchers to a notable amount.
Taking a look at single season home run leaders is notable as well. Of the 43 players who have hit 50 or more home runs in a single season, 27 of them did it within 10 years of an expansion of the game, and 7 did it exactly on an expansion season.
Roger Maris broke Babe Ruth‘s record in 1961 in an expansion year. Mark McGwire and Sammy Sosa had a ridiculous competition that broke Maris’ record in the 1998 expansion year.
However, it’s not just power, as the numbers above show. Historically, run scoring went down from the formation of the major leagues to the Black Sox scandal before heading up and really progressively moving up ever since.
It is notable that the first season of the major leagues, 10.47 runs were scored per game. In the most prolific single season of the 1993-2008 time period, scoring output was half of that.
It is also notable that during the prime of Babe Ruth, Lou Gehrig, and those dominant Bronx Bomber Yankee teams run scoring was actually higher on average than this time period. The thing that ended that time of offense was the second World War. From 1936 to 1943, run scoring dropped an astonishing 1.28 runs per game as players were called into service.
The game has ebbed and flowed in run scoring ever since, climbing nearly a full run from 1943 to 1950 to the point of averaging 4.85 runs per game. For reference, only 6 seasons of the 16 year run from 1993-2008 were even able to equal that number.
Run scoring in general has gone up for a time after expansion, then pitching will come back and reduce scoring, and then it seems that what happens is that rule changes take place (if not expansion) to help offense. This was the case in the late 1960s when standardizing the pitching mound made a huge difference as pitchers could have huge advantages depending on how their home team cultivated the mound with varying angles and heights.
Of course, just adding teams and depleting pitching doesn’t explain it all away. What about new ballparks?
Next: Ballparks