Baseball’s Great Hitting Barrage of the 1990s (and Beyond) Reexamined

In an article published in NINE in 2002, we examined what we called “Baseball’s Great Hitting Barrage of the 1990s.”¹ In addition to offering statistical support for the claim that there was an unusual amount of offensive productivity in the 1994 through 1999 seasons, we also considered explanations for why the hitting revolution had occurred. With regard to the latter, we questioned some of the popular theories for the offensive outburst—namely the “juiced-ball” hypothesis, the belief that ballparks were cozier in the late 1990s than they had been earlier, and the role of league expansion in diluting the quality of pitching. But at the same time we lent support to the arguments that lighter bats, physically stronger hitters, and a new style of hitting (with the assistance of a smaller de facto strike zone) contributed significantly to the great hitting barrage of the late 1990s.

Now is an especially opportune time to reexamine and update our earlier findings. Not only do we presently enjoy the benefit of a longer historical perspective on the 1990s, but we are also able to extend our analysis from the 2000 through the 2007 seasons. Furthermore, recent disclosures of the widespread use of performance-enhancing drugs by the players and Major League Baseball’s implementation of a drug-testing program in 2003 make it possible to employ statistics to better speculate about the effects of drugs on the great offensive barrage. Equally important to a reconsideration of the recent offensive outburst was the decision of Major League Baseball (beginning in 2001) to enlarge the de facto strike zone, determined by the umpires, and impose a more uniform strike zone on the umpires.

We reach three major conclusions. First, the great hitting barrage peaked during the 1999 and 2000 seasons. While remaining far above the two-divisional era in offensive productivity, the 2001 through 2007 seasons fell below the peak achieved in 1999 and 2000. Based on batting averages, runs per game, home runs per game, and on-base percentage plus slugging percentage, we posit three eras of offense in recent baseball history: (1) the two-divisional era of low productivity (1969–1993), (2) the great offensive barrage (1994–2000 seasons), and (3) the new equilibrium (2001–2007 seasons). Second, while it is impossible to offer quantifiably direct evidence of the relationship between drug use and the offensive explosion, we conclude that player use of performance-enhancing drugs did contribute to the hitting barrage. As the threat of exposure and then drug testing increased, some measures of offensive productivity began to decline, though not approaching the depths of the two-divisional era. Third, it is possible to offer more quantifiably direct evidence of the relationship between the strike zone and the offensive explosion than it is the relationship between drugs and offense. We conclude that the size of the de facto strike zone was an equal, and perhaps even more important, variable in explaining the hitting revolution as well as its modest decline after the 2000 season. When Major League Baseball decided to try to impose a more uniform strike zone on the umpires in the 2001 season, seasonal batting averages and runs per game (but not home runs) fell, though not back to earlier levels.

The Case for Three Eras of Offensive Productivity

Figures 1–3 provide the basic statistical support for dividing the offensive productivity of recent baseball history into three eras. In figure 1, notice the sharp ascent in batting averages for the 1993 and 1994 seasons; averages leveled off slightly for the 1995 through 1998 seasons, and then they lurched upward again for the 1999 and 2000 seasons. In 2001, batting averages began a sharp descent and remained below the averages from 1994 through 2000 until the 2006 season. Figure 2, which shows runs per game, follows a similar season-to-season trajectory.

Figure 3 demonstrates that home runs per game also jumped sharply in 1994 and continued upward to record highs in 1999 and 2000. In terms of fan involvement in the hitting revolution...