Does expansion meaningfully affect scoring?

It seems like a common notion among casual baseball fans that expansion boosts scoring. Certainly, the individual achievements that have happened in expansion seasons would appear to support this. Every time baseball has expanded, it seems, something noteworthy has happened, be it Roger Maris breaking the home run record in 1961, Mark McGwire doing likewise in 1998, or Rod Carew, John Olerud and Andres Galarraga hitting close to .400 in other expansion years.

Granted, the notion of expansion boosting scoring has its skeptics, most prominently perhaps Bill James who wrote in his 2001 historical abstract:

Expansion favors neither the hitter nor the pitcher, on balance; it does as much to create a shortage of good hitters as it does to create a shortage of good pitchers.

While I trust Bill James more than I trust conventional wisdom in baseball, his claim raised a red flag for me. With the help of the spreadsheet of baseball run averages since 1876 that I wrote about earlier this week, I applied a cursory test.

Expansion year League Average runs per team 5-year pre-expansion average Difference
1961 AL 4.53 4.36 Up 3.9%
1962 NL 4.48 4.39 Up 2.1%
1969 AL 4.09 3.8 Up 7.6%
1969 NL 4.05 3.89 Up 4.1%
1977 AL 4.53 4.04 Up 12.1%
1993 NL 4.49 4 Up 12.25%
1998 AL 5.01 5.05 Down 0.8%
1998 NL 4.6 4.6 Even

My thought? James is mostly right. Expansion alone won’t create a scoring boon, though it could favor individual achievement since the best players in baseball will face more marginal talents in expansion years. In his 1992 book Baseball’s Last .400 Hitter, SABR member John Holway suggested that in order for someone to hit .400 again, the majors might need to be tripled in size in order to restore player-population ratios of Ted Williams’ era.

That said, the fact that scoring has increased six of eight times that a league has expanded and didn’t meaningfully decrease the other two times is striking to me. I could drill down deeper in my research, though I’ll leave this as is for now.

3 Replies to “Does expansion meaningfully affect scoring?”

  1. Graham do you think that Holloway’s point might be a bit skewed if only due to the fact that in those days baseball was indeed by far the major sport where money could be made and drew a very large proportion of the talent that today goes also goes to other sports like Football and Basketball. The lack of African-American talent in the MLB for me is one indicator of the transition away from baseball to other sports.
    Had the likes of Willie Mays today come up as one example, he might have just as easily gone into the NFL as a QB. So perhaps would’ve Jackie Robinson as a running back. In both cases each man felt himself to be better at Football than the national pastime. No doubt there were others who excelled more so in other sports years ago, but saw the dollars and/or prestige of Baseball as a lure toward success and good fortune.

    1. Hi Alvy,

      That’s a good question. I don’t know if there’s a way to objectively answer that, though I’d assume there are a larger number of kids playing organized baseball these days. That has to count for something.


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