History tells us that expansion leads to an immediate spike in power and run production, which tapers off to more normal levels after a few years. The offensive numbers took off through two rounds of expansion in the 1990s, with Colorado and Florida joining the National League in 1993 and Arizona and Tampa Bay added to the majors in 1998.

In 2008, however, the power dipped to its lowest levels since 1993, the inaugural season for the Rockies and the Marlins.

MLB’s Lowest Runs/Game, HR/Game, Slugging -- 1993-2008

. Yr. . . . . . .R/G. . . . . . . . . . . . .Yr. . . . . .HR/G. . . . . . . . . . Yr. . . . . . SLG
2005. . . . . . 4.59. . . . . . . . . . . .1993. . . . . .0.89. . . . . . . . . . 1993. . . . . .403
1993. . . . . . 4.60. . . . . . . . . . . .2008. . . . . .1.00. . . . . . . . . . 2008. . . . . .416
2002. . . . . . 4.62. . . . . . . . . . . .1995. . . . . .1.01. . . . . . . . . . 2002. . . . . .417
2008. . . . . . 4.65. . . . . . . . . . . .2007. . . . . .1.02. . . . . . . . . . 1995. . . . . .417
2003. . . . . . 4.73. . . . . . . . . . . .1997. . . . . .1.02. . . . . . . . . . 2005. . . . . .419

The runs per game in 2008 weren’t as far off recent seasons as the homers and slugging. Home runs have been down each of the last two seasons, compared to 1.11 homers per game in 2006, which is closer to the 1.08 average for the decade.

This writer knows what many of you are thinking. It doesn’t require ESP (or ESPN). It’s easy to assume the juice is the difference, and most likely it’s a part of the equation, but it’s not the full story.

Performance-enhancing drugs have probably been given too much credit for the power surge of the last dozen years or so. Expansion has played a role in it, and no doubt the plethora of smaller ballparks that have been built in the last decade has made a difference. A decade ago, there was a lot of talk about the ball being juiced, and that very well may be true, but that idea’s been lost in the noise about juiced players.

The game is a 133-year battle between hitter and pitcher, and both have had to make adjustments during eras that favored the other. It’s a never-ending process, baseball’s version of survival of the fittest.

It may be that major league bullpens have helped turn the tide against hitters, particularly in 2008, when run production was down and strikeouts were up. The specialization of the bullpen is part of the game’s evolution, and it seems to be making a successful adaptation.

MLB Batting & Bullpen Performance, 2006-08

. . . . . . . . . . . . . . . .2006. . . . . . . 2007. . . . . . . . 2008
Hitters’ K Pct. . . . . .16.8. . . . . . . . .17.1. . . . . . . . . 17.5
Runs/Game. . . . . . . .4.86. . . . . . . . .4.80. . . . . . . . . 4.65
SLG . . . . . . . . . . . . .432 . . . . . . . . .423. . . . . . . . . .416

Bullpen ERA. . . . . . . 4.20. . . . . . . . 4.16. . . . . . . . . 4.08
Bullpen OBA . . . . . . .259. . . . . . . . .256. . . . . . . . . .254
Bullpen K/9. . . . . . . 7.29. . . . . . . . .7.35. . . . . . . . .7.52

There may be other on-the-field factors in the power downturn as well, though that’s a subject for another researcher.

The key point is that when it comes to the dropoff in power, what goes on down on the field isn’t as obvious to identify as a contributing factor, certainly less so than an easy target such as steroid use. The game keeps evolving as both hitters and pitchers continue to adjust to each other and the conditions in which they play.