With Mark McGwire’s recent admission that he used steroids throughout the 1990s, there has been a resurgence of chatter regarding how to view the performances of the past 15–20 years. But, I think it’s wrong to attribute most of the high home run rates of this time-frame to steroid use. The connection that many people want to make is understandable. We have evidence that many players were using steroids during this era, and steroids have been shown to increase strength and power; therefore, it should follow that home run rates should rise accordingly. (And let me make this clear before I move to the next step: I believe wholeheartedly that steroids are effective ergogenic aids to baseball players—it’s growth hormone that does nothing.) However, I do not think steroids are the main cause of the dramatic rise in offense (particularly the home run) in the 1990s–2000s.
Why do I think this? Take a look at the following graphs. The first maps home runs per game from 1921 — 2009.
It’s clear that the present era is different from the past, but I also think it’s interesting how quickly it changed and did not change. In 1993, home runs per game jumped by 23%, and in 1994 they jumped 16%. Since that time, the average absolute change in home run rates has averaged about 5% and maxed out at 9%. Home run rates rose, then plateaued. The graph below zeros in on home runs per game since the 1990s.
If steroids were the cause of the steroid era, then we should have gradually seen them enter the game. A few players use and then others slowly adopt their technique. But that’s not what we observe. Almost overnight, home runs jumped. If you want to believe home runs are largely responsible for the change then you have to believe that players all got together in 1992 and 1993 and said, “hey, it’s juice time.”
But even more convincing in my mind is the fact that the home runs haven’t gone away with steroid testing. In 2005 (marked by a vertical line on each graph), Major League Baseball began drug testing with suspensions, and the home runs didn’t go away. You might be able to look at the graphs and identify a slight decline—it’s difficult to separate the noise from real changes with so few observations—but it’s clear that home runs aren’t close to their pre-1993 level. Yes, tests are imperfect and can be beaten, but the dramatic change in enforcement—from no monitoring or punishment to strict monitoring with punishment—ought to yield more substantial declines. Do I think steroid testing has taken away some power from its users? Absolutely, and it barely shows up in the aggregate data. In my mind, the rise must be attributable to something else. And if you think Ken Griffey had two seasons of 56 home runs without the help of steroids, then it would be useful to have an alternate theory.
So, if steroids aren’t the cause, then what is? I have a few theories.
1. MLB changed the ball. I have little doubt that the league allowed (or introduced) a lively ball into the league. This would have the effect of boosting home runs for all players. Certainly, I can’t prove this, but there have been whispers about it for years. This theory explains the dramatic rise in home runs and the lack of decline after testing.
2. Expansion. Baseball expanded by two teams in 1993 and two more in 1998. As I have detailed before (see here and here), as talent became diluted, excellent performances began to happen as the very best (hitters and pitchers) were able to take advantage of the very worst. The abrupt change in home runs fits exactly with the timing of expansion. Joe Posnanski also discussed the the possible influence of expansion (as well as a few other explanations) in a recent column.
3. New stadiums. Smaller parks and home-run alleys may have caused more home runs to fly out of the ball park. While, on balance several new stadiums are home-run-friendly (Colorado) others have dampened home runs (San Diego). Given the dramatic spike in home runs, I don’t believe this could have had more than a minor effect on home runs, and the effect would occur gradually.
4. Bats. Bat technology has certainly changed since I was a kid, when nearly every player used an ash bat made by Louisville Slugger. Maple bats, hardened with shellac, with tiny handles are the new weapon of choice for batters. Again, I think this fails to explain the home run spike in the early-1990s, because they trickled into the game. It could be a contributor, but it’s not sufficient on its own.
5. Strike zone. It’s possible that the league redefined the strike zone into a more-compact area to increase offense. However, recent attempts to expand the zone (with the help of computer monitoring) haven’t dampened offense.
There may be a few explanations that I have missed, and I’m open to others. But if you have another hypothesis, it must be able to explain the near-instant rise and subsequent plateauing of home run rates. I believe steroids fail this test miserably. I’m fine with the “home run era,” but in my mind steroids can only explain a very small part of why home runs increased during this time period.