Tango on the 1992-94 home run explosion
There was a large increase in major-league baseball hitting in 1993 and 1994, one that continues today. In 1992, there were 0.721 home runs per game. In 1994, there were 1.033 home runs per game. It wasn't a one-time increase: the 1994 rate has pretty much stayed with us to the present day.
What happened? There are various theories. One says that the 1993 expansion brought in a bunch of inferior pitchers, and the dilution of talent caused the numbers to jump. Another theory says that it's the ballparks – Coors Field entered the National League in 1993. A third theory says it's the ball: it was juiced up around that time, and remains juiced today.
In a post about a year ago, I argued that expansion couldn't have caused an effect as big as the one we saw. With reasonable assumptions, you can show that expanding by two teams should cause home runs to increase by only 3%. And you could also do the same for ballparks – even with Coors Field now in the equation, and even combining that with the 3% for expansion, there's still no way you can explain the 40% increase in home runs.
But for those who don't follow that logic, Tom Tango has an excellent study that should now win over the unconvinced.
Tango looked at the 1993 season, and compared it to 1992. But he stripped 1993 down, considering only players who played in 1992, in parks that were in existence in 1992. And he adjusted all the players' stats to give them equal playing time in 1992 and 1993.
The results: even among the incumbent players and parks, there was an 18% increase in home runs.
Repeating the study for 1993/1994, Tango found a second increase, this time of 20%.
Over two years, even without the effects of expansion, and the effects of new parks, there was a 42% jump in home runs.
So it can't be the parks. And it can't be expansion.
I don't think this finding is a big surprise, but it's so thorough, and so understandable, that even non-sabermetric fans should be convinced. You'd hope.
Anyway, if it wasn't the parks or expansion, was it the ball? Tango presents convincing evidence to say it was.
According to Dr. James Sherwood, MLB's ball tester, minor-league balls travel 391.8 feet under the same conditions that major-league balls travel 400.5 feet, for a difference of 8.7 feet. And, according to Greg Rybarcyzk of HitTracker Online, if you eliminated all home runs in 2006 that cleared the wall by less than 8.7 feet … you'd have roughly the same home run rate as before the jump.
I think Tango has found the answer.